All our experience of external things is provoked in us through the organs of sense, and since we have no enjoyment of ourselves which is not the contemplation of a non-mental object, all our experience whether enjoyed or contemplated is provoked through the sense-organs. The most complicated objects or enjoyments are resoluble into elements of sense, or its derivative idea, and their groupings in some empirical plan, and from beginning to end these experiences are qualified by categorial as well as empirical features. Moreover, not only do our categorial experiences come to us through the medium of sense, but those senses are the organs for the secondary qualities of matter. I speak at present of the special senses and not the organic and kinaesthetic ones. We do not see or feel or otherwise experience Space or Time except through vision or touch or some other apprehension of secondary qualities. The primary qualities which are empirical differentiations of Space and Time never reach our minds, as Berkeley saw, except along with secondary ones. The nearest approach we have to a hint of the separation of them in our experience is found in the fact that a thing may be detected further to the side of the field of view or with a fainter intensity, when it is moving than when it is at rest. But though our experience of Space and Time is thus provoked in us through sensation it does not follow and it is not the case that they are apprehended by the senses. We have first to ask how the mind apprehends Space and Time and with them the categorial features of things. The apprehension of the primary qualities offers no particular problem when once we know how Space and Time are apprehended, and in fact we only immediately apprehend Space-Time and its fundamental characters the categories in their empirical determinations. To apprehend Space-Time as such, and as a whole, and the categories as such, we have to add reflection to our immediate apprehension.
Intuition of Space and Time.
We were content in an earlier book to distinguish categorial from empirical characters as belonging to all existents alike. They were enjoyed in minds and contemplated in external things and existed equally in both. But now that minds are seen to be compresent with things and thereby to have cognition of them, we can see further that not only are the categories features of both minds and things, but that the mind enjoys itself categorially in contemplating the corresponding categorial feature of the object which it contemplates. Let us confine ourselves in the first instance to Space and Time as such, and for convenience treat them in abstraction one from another. In being conscious of its own space and time, the mind is conscious of the space and time of external things and vice versa. This is a direct consequence of the continuity of Space-Time in virtue of which any point-instant is connected sooner or later, directly or indirectly, with every other. That relation was described more explicitly by the hypothesis that the instant performed to the point the office of mind, and that in an extended sense of ‘awareness’ each point (to confine ourselves to Space) might be said to be aware of every other in the way in which minds are aware of one another.
For clearness' sake let us take a particular case and suppose a line of colour ab which we see. It excites through our eyes a certain spatial tract in the visual region (not necessarily a line or even a continuous tract), and that neural excitement of the centres is the consciousness of colour. Call the neural tract AB. The points or other parts of it are, as merely spatial, ‘aware’ of ab. Moreover, they are aware, in the same extended sense of ‘awareness,’ of the points in ab as being the origin of the whole transaction of light-movements which connect those points with the corresponding neural centres. Thus for example A is aware of a in general just as it is aware of every other point. But it is also aware of a as the beginning of the line of advance which ends at itself. A line of advance, in the pattern of a movement of light, which started from a different point would not at the same moment end in A but some other brain position. Now if there were no consciousness belonging to the excitement of AB, our minds would know nothing of the place of ab. That knowledge would belong to those brain centres merely as points of space; much in the same way as when something is behind our back, which we do not see, that object is still ‘apprehended’ not by our mind but by our body. And the knowledge would not be of the order of contemplation but would be comparable to the kind of assurance we have of one another's minds. But AB is a conscious excitement and contemplates the colour ab. Now that consciousness of colour is (or contains) the conscious enjoyment of the spatial tract AB. Thus we have AB conscious and the mind is therefore conscious of, that is contemplates, the tract ab as spatial and in its locality in space. Though the brain centres are excited only by visual stimuli, the excitation is that of a space already ‘aware’ as merely spatial ‘of’ its definite connection with AB according to special and definite lines of advance. Lifted into conscious enjoyment through the sensory excitement, that space is now aware as consciousness, or consciously, of the non-mental or external spatial character of ab.
To put the matter shortly, a space which enjoys itself consciously or menially as space contemplates the space of the object, or rather has for its object an external, non-mental, contemplated space, contemplated that is in its form and position in total Space. And as we cognise the colour as a sensum in the act of response to it which issues in movements of the sensory organ or other motor action, so likewise in this response we contemplate in addition the place of the colour. According to the place of the colour excitement, these motor issues are specialised; the eye or hand moves to the right or the left. Yet this specialised response remains a response to the sensory, tactual or visual, excitement and is not, as it were, the response to a place-sensum. It is part and parcel of the machinery for apprehending and sustaining the apprehension of the sensory quality. For our responses to things are practical actions designed to obtain or avoid things in virtue of the qualities they possess. If the eye moved to the right when the illuminated point is to the left the colour excitement would be lost. The specific motor-response in which the pattern of colour-sensing issues according to its place in the brain is still a colour-response, designed to fixate the stimulus, not a place-response. It is only a place-response in so far as it forms part of the visual response, and the apprehension of the place remains different from the sensing.
It is convenient to defer the fuller consideration of the apprehension of Space till we can consider the secondary qualities. I need only note here that according to the present doctrine there is no need for any specific local sign belonging to a visual or touch centre, whether that local sign is conceived to be central in its character or peripheral. The place of the brain centre is sufficient as the basis of apprehension of the place from which the stimulation proceeds. Finally, there is no assumption that the brain space AB in any way resembles the external space ab nor that if ab is apprehended both by touch and vision, the space AB of the visual region at all resembles in shape that of the tactual region of the brain corresponding to the same external shape ab. Whatever group of places in any sensory region of the brain is excited to consciousness by the external thing, the enjoyment of that space is thereby the contemplation of the space and place of the stimulus sensed. The places excited in the touch region might be spread out over twice the extent of the places in the visual region, and to a square object there may correspond a fantastically irregular geometrical distribution of brain places; the result will be unaffected. The shape and extent of the brain affection depends on the sensory arrangements of the brain, not on the shape and extent of the object.
The mind therefore does not apprehend the space of its objects, that is their shape, size, and locality, by sensation, but by a form of apprehension simpler than sensation, for it depends for its character on mere spatio-temporal conditions, though it is not to be had a consciousness in the absence of sensation (or else c course ideation). It is clear without repeating these considerations that the same proposition is true of Time and of motion in which the space and time elements of external things are inseparably united; that the enjoyment of the date and duration of mental events is the contemplation of the external time and duration of their objects; and similarly for motion; and that this apprehension too is not had without sensation but is anterior to it. At the risk of attaching a new interpretation to a much used and misused word, I shall call this mode of apprehension in its distinction from sensation, intuition.1 We contemplate Space-Time and Space and Time intuitively and we enjoy it intuitively. Intuition corresponds to that “bastard kind of reasoning”2 whereby according to the speaker in the Timaeus the soul apprehends Space, the matrix of things. Only I repudiate the depreciatory adjective “bastard.” Intuition is different from reason, but reason and sense alike arc outgrowths from it, empirical determinations of it They are its legitimate children. And as a father may learn from his child, reason may clarify the intuition, as it does in the practical working of the mind in everyday life or in the exercise of philosophical speculation, as the present investigation illustrates in the measure of its capacity. It is thus the intuitively enjoyed which is cognisant of the intuitively contemplated.
Cautions against misunderstanding.
Every sensory act contains in itself, and consequently conceals or masks, a simpler act of intuition. The brevity of this statement may lead to certain misunderstandings which it is desirable to remove, even at the cost of excessive detail. How, it may be asked, do we know that the place we are aware of as place is the place of the colour or the touch? We do but refer the colour sensed to the place intuited, and how is this co-ordination effected? Now in sensing a colour we have not two separate acts of consciousness whose objects we refer to one another. There is no separate consciousness of the place, to which to refer the colour; for the consciousness, or intuition, of the place is only excited so far as we have the sense of the colour. The monad or point-instant by itself has no consciousness; though it has awareness in the extended sense of that word, which does not imply the existence of mind but only of something which performs the office of mind. Consequently there are not two acts of mind but only one act of mind, which in its sensory character apprehends the colour, and in its intuitive character apprehends the place of it. We are conscious of a place coloured or of colour in a place. The monad's excitement exists as conscious only in so far as it is taken up into the sensory excitement of the place of the reception of the sensory excitement. To be aware of the colour, and in and by the same act of a place, is to have revealed to the mind the place of the colour.
I have deliberately neglected for the present the problem which arises from the variability of the spatial appearances of things, like the shrinking of a plate to sight as it recedes.3 But a general remark may be made here, because of its importance, which follows from those of the preceding paragraph. If in seeing a colour we intuite its place, it is equally true that we intuite the place only so far as we see the colour. Consequently whatever makes the sensory excitement in the brain indistinct, by which I mean numerically indistinct, wanting in individual separateness, affects the intuition of the place of the sensum. Such indistinctness may consist in diffusion of the sensory excitement, as when a point of light is seen by the unaccommodated eye as a halo. Or the indistinctness of the sensation may betray itself by confused or diffused movements of reaction of the organ or body. Such indistinctness in the sensory reaction according to the place excited in sensing would mean a corresponding indistinctness in the intuition of the place of the sensum.
Minor difficulties may be met upon the same lines. Why, it may be asked, if the brain-patch AB is aware of the lines connecting it with a colour-patch ab, do we not see these lines as well as the patch itself? The answer is that the lines of light are not coloured. If a mote is in the way which they illumine, this we do see. Or it may be asked: since the monad taken up into conscious awareness by a sensory excitement knows the place and the spatial characters of the sensum, why then are we aware of a colour simply as colour, and not aware along with it of the movements in the coloured thing as well as of the vibrations of the ‘ether.’ Locke indeed would have no difficulty in answering that we fail to recognise these movements because of the coarseness of our senses, and that if we were as delicately sensed as the angels we should see them, and the secondary sensations would accordingly disappear. Such an answer lies completely outside our view, because the primary qualities are not objects of sensation at all. But the real answer to the question follows the lines of the previous answers. The vibrations in the coloured body are ‘apprehended’ by the monad, or it is aware of them, so far as it is purely spatio-temporal. But in order that they should be apprehended in consciousness the sensory scheme must be present also. Now in seeing colour the sensation is of colour. There is no visual picture of the movements in the body which underlie the colour. Thus the monad which is conscious of the place of the colour has no consciousness of the constitution of the colour stimulus though it is aware of it in the extended sense of that word.4
The unity of mind.
Before proceeding further I can now revert to the problem left over from a previous chapter5 of how we enjoy our mental unity in spite of the unfilled gaps in mental space and time, and with the consciousness that there are such gaps. Hitherto I have been speaking of the intuition of external spaces and times. But the same considerations apply to our enjoyments. I wake up from dreamless sleep to see the light streaming through the blinds and am aware that I am the same mind as enjoyed last night reading Molière before I slept. Let the present enjoyment be A and the remembered one B. The point-instants of A and B are through the mental excitement lifted up into conscious enjoyment of their own mental places and times, and they also have ‘assurance’ (in the wider sense) of the intermediate point-instants. It was comparatively easy to see that any mental event contemplated intuitively the place and date of its object and the rest of Space-Time. It is not so easy to see that A enjoys the interval of mental space-time between itself and B. If B were a foreign mind, A would merely have assurance of B's mind and contemplate its place and time. But B is not a foreign mind, and is enjoyed as well as A, and the two point-instants are enjoyed together. Thereby the intermediate point-instants between those of A and B are lifted up into enjoyment, just as before the assurance which a point-instant had of the place and date of the object and all other point-instants was lifted up into contemplation. The assurance which the point-instant A or B, as a mere point-instant, has of the intermediate stretch of space or time modifies the two enjoyments which are together, and these stretches are enjoyed. Only they are not enjoyed as A and B are; there are no mental events to fill the empty stretches. They enter into the enjoyment not as memories but as modifications of the present enjoyed event A and the past enjoyed event B; in the same way as in perception of an object the past experience of it modifies the present object without being an actual memory. The time-gap (and the same is true of the space-gap) is contained in the enjoyment without being filled with mental events. And this agrees with the common apprehension we have of the gap in time, of which all we can say is that there is such a gap, and nothing more. The subsidiary experiences which were mentioned in the previous passage come in to inform us how the gap was filled, if it was filled at all, with mental events. We are merely aware otherwise that there has been a gap between our event A and our memory B and that the gap is mental. This is to enjoy the mental gap and enjoy our mental unity.
Intuition and enjoyment of the categories—Substance.
What is true of Space and Time is true equally of the categories which are but fundamental characters of Space-Time. Not only have minds equally with external things categorial characters, but we enjoy the categorial characters of mind in the act of contemplating the corresponding categorial characters in the object. We are aware of ourselves or our acts as having intensity in so far as we contemplate intensity in the object and not without such contemplation; we are, or enjoy ourselves as, substances in cognising external substances, in thinking or intuition of a number our enjoyment has number. It would be tedious to pursue this proposition through all the categories. Some remarks, however, seem desirable in the case of the two categories of substance and causality, more particularly the second. One point of difficulty is common to both, and may be removed at once. Our mind is always substantial even in a single act, and it is also substantial as a whole. There is a substantial coherence between all its acts, and within this larger whole of mind there are smaller substantial groups of cohering activities. This corresponds to the separation of substances in the external world which itself is, though only in a metaphor, one great substance. It is experience guided by scientific method which teaches us what objects cohere together more closely; and in correspondence therewith we learn that acts of mind which may be present as a matter of fact contemporaneously and do belong together within the one mind, do not otherwise belong together. Thus the various acts cohering together within the substantial experiencing of an orange do not cohere closely with the experiencing of a chair on which I am sitting. In the same way, in causality, some acts of mind lead on by way of causality to others as in ordinary association of ideas, but they are prima facie unconnected with others occurring at the same time, though there is some causal reason in the whole mind for their appearing there simultaneously.6 Experience teaches us to correlate events in the external world with one another as cause and effect and to treat other connections in space and time as not causal but as we say accidental. Similarly with the corresponding mental acts in which the events are apprehended. There is ultimately some direct or indirect causal connection between all finites. But the connection may be highly indirect.
Now there is no special difficulty in recognising the truth of the proposition laid down, in respect of substance. But causality offers peculiar problems, and both on its merits and on account of its philosophical history causality is at once the hardest and most instructive of the categories to study in detail. Causality is contemplated most obviously in observing the causal sequence of two external events; and enjoyed most obviously in observing the influence of one thought in our minds over another, as when thinking of Raphael leads me on to thinking of Dresden and the Sistine Madonna; or as when we actively suppress an idea. Yet it seems at first blush paradoxical to hold that our minds enjoy their own causality in following an external causal sequence, and still more that in influencing the course of our thinking we contemplate causal sequence in the objects. Again, when we are willing an external change and feel ourselves active, the beginning of the process seems to be enjoyed and the end contemplated. How can the formula apply in such a case?
A little inspection dispels these doubts. Causation, we saw, was the continuous connection in sequence of two events within a substance. In contemplating the action of the wind in blowing down a chimney, we enjoy first the act of contemplating the blowing wind and the standing chimney, and this enjoyment passes continuously into that of contemplating the fallen chimney and the wind passed by.7 We pass in enjoyment through mental processes corresponding to this determinate connection, and though each stage in the enjoyment is provoked from the outside, there is the experience which is characteristic of causation. It only seems strange to say that the first enjoyment causes the second in such a case because the enjoyments are not initiated from within, in which latter case we say without reserve that we are the cause of the next enjoyment. But seeing the chimney fall when the wind blows against it with sufficient strength flows from observing the wind blowing and blowing against the chimney, and arises out of the first act of mind, so long as we continue to observe and our minds are thrown into the attitude of receptivity to nature. The second act is the fulfilment of the first when the first is taken in its completeness. When we do not see, we expect, provided we have seen before; and in fact when Hume declared our experience of causality to be the consciousness of the expectation, he was saying something true and vital, though he used it metaphysically in a different way from ours. We may thus be aware of causality within our enjoyments though no part of the process is initiated by ourselves. We only miss this so far as we take the wind and the chimney by themselves; but we cannot miss it when we take the two events as a determinate sequence within the substance of which wind and chimney are both parts. Or we may miss it, if we think causality to mean that the observing of the wind blowing against the chimney has some mysterious force in it to produce observation of the fallen chimney, whereas it only means that the one observation is felt to be continued into the other.
On the other hand, when I actively suppress a thought like the thought of striking a person who has annoyed me, there is clearly enjoyed causality, but also the non-mental object which comes first, namely, the hindered attempt to strike the man, is in causal connection with the object, the man uninjured. Only here the contemplated objects are all ideal and may have no sensible correspondent in the perceived world, and the causal relation contemplated is equally ideal. I may call up the spirit of Plato to unfold the habitation of the soul (pardon me, shade of Milton, the abbreviation!), and Plato in my dream tells me his message as he would in reality. When thinking of Dresden makes me think of Raphael, so that I feel my own causality, Dresden is not indeed contemplated as the cause of Raphael, but Dresden and Raphael are contemplated as connected by some causal relation in the situation which is then my perspective of things, so that there is some reason for their being together and not merely for my thinking them together.
Lastly, when, in the mixed variety of causation, I will to strike a man and strike him, I am enjoying causality as the determinate sequence of my perceiving of him struck upon the ideation of striking him; but on the object side there is the equally causal transition from the external preparation to strike to the actual blow. But here the beginning of the whole enjoying is initiated in mind and the end is provoked by the object. Thus causality stripped of all adventitious notions of power may be enjoyed whether it is actively initiated or guided passively from the object, or half one way and half the other. The consciousness of activity adds to that of simple causality another element, that of self-initiation. “This making and unmaking of ideas,” says Berkeley, “doth very properly denominate the mind active.”
Causality as between mind and things.
The experience of willing in which an idea in the mind (whether it be a free or a tied idea) results in a change in the external world, and that of sensation in which a mental act is the effect of an event in the external world, introduce us to a fresh intimacy between mind and its object in respect of categories, that is to say as regards the mind's intuitions. Not only is a category enjoyed along with cognisance of the same category contemplated; but since the mind and its objects are compresent existents, there are also categorial relations between mind itself and the objects. Thus not only does mind enjoy its own space through intuition of its object's space, but the enjoyed and the contemplated spaces both belong to the same Space. The same is true of Time. In the Introduction8 we saw that inspection of experience shows that we are aware of ourselves as in the same Space and Time with our objects. We enjoy our togetherness with them in space and time. The togetherness itself, as we saw, was enjoyed and not contemplated. If we contemplated the object as together with us, we should also be contemplating our minds as the other end of the chain, and we cannot contemplate our minds. The enjoyer and the contemplated are in fact two existents in one Space, and this togetherness is experienced by the enjoyer in enjoyment. (In the extended sense of the word, the object in turn ‘enjoys’ its compresence with the mind, that is with its non-mental basis or equivalent.)
Similarly the mind not only enjoys itself as substance through intuition of an external substance, but it belongs to the larger stuff of Space-Time which comprehends it and that external object. In like manner our mind and external things are, as compresent existences, in causal relation to one another, and we enjoy ourselves as causes in respect of the things we affect and as effects of the things which act upon us, as they do primarily in stimulating us to the act of sensing. Indeed, as Mr. Stout has made clear, it is the experience of our manipulation of external things which is the immediate source of our consciousness of causality, and I add that we use this experience of causality in ourselves not to discover causality as between things but to interpret it and realise its meaning. Simple inspection of experience assures us that in voluntary or impulsive action we are aware of ourselves as causal in respect of things, or active, and that in sensation we are passive in respect of the sensum; and once more it accords with the results of our hypothesis.
It has sometimes been affirmed that in sensation we must postulate that there is an object which causes the sensation.9 Postulates are to be regarded in metaphysics with the deepest suspicion; and no postulate is needed for what experience, which is our only ultimate test, asserts. We only need to explain more precisely the nature of the experience. We enjoy our sensing as the effect of the sensum, and this enjoyment has the characteristic vivacity of all sensory experience. To enjoy ourselves as the effect of the sensum is the whole experience we have of the causal relation between the sensum and ourselves. We do not contemplate the sensum as the cause, except in this sense. To contemplate it as cause in the same way as we contemplate it as the cause of some other external event, would be either to contemplate ourselves as effect, which is impossible, or to experience the relation of causality twice over, first as contemplated and then as enjoyed. This is but repeating what was said above of togetherness in space and time. To enjoy ourselves as effect of what we contemplate in sense is the experience we have of the relation of causality where one of the partners is an external existence and the other an enjoyed one. Similarly when we act upon the external world we are enjoying ourselves as cause, not of course of the immediate object of our ideation (this has been commented on already) but of the change we produce in the thing, and when that change is produced we become, in sensing it, in turn effect towards it.
At the same time this discussion helps to reinforce the truth of the fundamental principle of cognition that the object is revealed to us and that it is in no sense in the mind. It might be urged that, after all, the effect of the external object upon us is a brain process, and, since that is not known to us in the act of sensing, we are not aware of any causal relation. This objection would be much in the spirit of Hume's famous criticism of the assertion that we are aware of causality in the act of willing. But it is at once irrelevant and helpful. It is irrelevant because the neural effect though not known is identical with the conscious enjoyment which we have. And it is helpful because our ignorance of the neural effect and our enjoyment of the corresponding (and identical) act of consciousness compel us to see that what we know or contemplate is the object itself directly and not the effect it produces in us. Thus the sensum which is the cause of the sensing is not experienced by the patient as the effect which it produces in him but is experienced in and for itself as what it is contemplated to be, and, in our language, is revealed to the patient. The patient is not cognisant of the effect but is it; he is cognisant of the object which is the agent. Hume was right in seizing on the problem of causality as the vital question in knowledge. It is reflection on causality which is the best, if not the most obvious way, of approaching the whole problem of the nature of knowing.10
Thus the categories obtain not only as between external finites or between acts of mind, and not only are they enjoyed in the actual contemplation of the same categories in the external world, but they obtain as between a mental and a non-mental finite; as should be expected in accordance with the whole principle of explanation, which in its turn is attested by direct experience.
It must be added that though we only enjoy causality or other categories so far as there are external objects to be known under those categories; the converse proposition is not true: namely, that there are external things under the categories only so far as there is corresponding enjoyment in us under those categories. Finites below the level of mind and before the emergence of minds in the order of empirical history stand in categorial relations to one another though there is no mind to know them. Only they are not consciously experienced.
Apprehension of matter.
Of the primary qualities of matter nothing further need be said in this connection. They are empirical determinations of Space and Time and motion, and are apprehended by intuition. But the answer to the question by what kind of mental act we apprehend the materiality of matter, which as I have supposed includes its mass and energy, is one of great difficulty. The question is not of the reality of matter. Matter is not the only reality; the mind too is real and is not apprehended as material; for the materiality of the material basis of mind is not a categorial character and is not carried up, like those characters, into the enjoyment. But if I am right in thinking that materiality is really an empirical quality of a certain level of existence, though resoluble like all empirical qualities into modes of Space-Time, we have to identify the apprehension of it amongst our modes of mental action. It is, I think, apprehended in the sensation of resistance offered to our bodies. The sensum which we are aware of in feeling resistance is a complex one. Primarily resistance is one of the kinaesthetic sensations and closely related to the organic ones, and it has for us another interest as well as the present one, namely, in its connection with life.11 But in the sensing of resistance I not only sense my own body but also the opposition to it of something or other which resists. That something or other is the materiality of the foreign object. The sense of resistance is not so simple as the sense of motion in my joints or that of hunger or thirst. In them I sense my body alone, and as we shall see as a living thing. In sensing resistance I sense the strain in my body, and I sense it not as something material but as a determination of my ‘life’; but also I sense the something which resists. And the whole situation is mediated through touch, which, however, only lets resistance in to our minds as colour or touch itself lets in categories like Space and the rest. The significance of the sense of resistance seems to lie in its thus supplying the link of connection between one very intimate thing, my living body, and another and foreign thing, matter.
Inertia as commonly understood implies on the part of matter resistance to any attempt to change its condition, whether of motion or rest. Having learnt in the case of our living bodies what this resistance of a foreign body is, and through the mediation of the secondary sensation of touch, we understand what the inertia of a material body is as displayed in its relation to another body not ours, when that situation is revealed to us by sight and not by touch. We have then an illustration of how something experienced directly in one experience may be used to interpret a different but allied experience. For it would follow that if matter is apprehended in its materiality by resistance felt through touch, sight does not itself reveal materiality, but a seen object is cognised as material through reference to what is learnt, not indeed by touch but by resistance provoked through the medium of touch. This agrees with our common experiences. For when we see colour we do not see materiality but colour. It is true that colour does as has been described reside in matter, but as colour it is not matter. The materiality of what is coloured is not carried up into the higher level of empirical existence which is colour.
In identifying the sense of resistance as containing the apprehension of materiality, I am having recourse to a form of sensation which in older theories of knowledge and of psychology played a large part, but has fallen now into something of discredit. There is no peculiar revelation of reality, it is urged, which is conveyed to us by this kind of sensation. And it is quite true that the resistance of a thing when we touch and push it no more teaches us the reality and independence of the thing than any other sensation. It is only one instance or how we come to be aware that there are things to which we must adapt ourselves, and which we have to humour, so that if we desist we lose them, as I should lose the table if I continue to move my fingers on in the direction of its edge beyond the corner where the edge turns at right angles. This happens to me equally with colour where if I turn my eyes away I lose the colour. But, to repeat myself, I am not suggesting that the sensing of resistance has any prerogative to inform us of reality; but only that it informs us of the empirical quality of being material. If I am right it does supply not a peculiar but a special revelation of that.
Apprehension of secondary qualities.
The primary qualities are apprehended by intuition but through sensation. The secondary ones are apprehended by the specialised empirical forms of spatio-temporal mental response of the special senses. We have seen that each act of sensing has its intrinsic extension which is the pattern of the response. Correspondingly the sensum has its intrinsic extension, which is its extensive pattern in the external thing, but it is not apprehended in the act of sensation as extensive but as the quality of the sensum, blue or hot or sweet or hard.
Intrinsic extension and extent
The place of the sensum and that of the sensing are, to speak strictly, not part of the intrinsic extension but are intuited, and are extrinsic to the sensation in so far as the sensation has sensory character. Hence it is that while in the sensing the pattern is purely spatio-temporal, in the sensum it is a quality, but the place of the sensum (not necessarily or indeed ever a geometrical point) is apprehended, as all purely categorial characters are, in correspondence with the enjoyed place of the sensing. The intrinsic extension of sensation is thus to be distinguished from the extrinsic extension of sensation, which is what is commonly called its extension, but does not belong to it in virtue of its quality (that is, its occupying space according to a certain pattern) but in virtue of its occupying a space in the sense of greater or less repetition of that pattern in space. The greater or less extent (to describe the extrinsic extension by a special word) of sensory experience depends on the greater or less space which it fills, that is to say on the multiplicity of the sensory objects or enjoyments. A blue thing is blue as a whole because the blue material processes are spread over the area of the thing when it is subject to the action of the light. And as we have seen the blue does not fill the whole area but is stippled over it in more or less density, leaving room for those processes which are sensed with other sense-qualities.12 A single point of blue colour is nothing but the smallest area filled with that quality, and the place of such a point is thus the minimum sensibile of extent which is coloured blue. The whole extent of the area is seen coloured because the sensory qualities which provoke our intuition of their places are not finely enough delimited from each other. Under the microscope this discrimination may occur and the blood which seems red to the naked eye is seen as a yellowish extent in which red corpuscles are seen separately. At the same time such undistinguished sensation of a coloured area is possible because the space of the area is itself continuous and is so apprehended in our intuition. What is true of the sensed colour and its extent is true also of the sensing of it. A larger area of vision is a larger extent of enjoyed space in the neural region engaged, and the separate points of vision are not enjoyed separately because, as we must suppose, the excitement provoked by sensation in those points spreads over the intervening places.
Intensity of sensum intuited.
The place of a sensed minimum forms the transition between the intrinsic extension and the extent of sensory experience. The place is the lower limit of the extent. At the same time, even the minimum sensed has intensity, and intensity seems at first sight to belong intrinsically to a sensation as sensory. It is probably referable as we have seen to the spatial density of the sensum, that is the filling of the place in the same time. The notion of density was illustrated by Mr. Brentano by the paling of the red in brightness when red points are scattered sparsely over an area otherwise black.13 And within a minimum of intuited extent we have according to the intensity a varying density with which the sense-quality fills it, and this density apprehended not numerically or extensively but taken in at once in the act of sense and integrated in the actual external fact as the intensity of the sensum, to which corresponds that of its sensing.14
It seems very difficult to separate the intensity of a sensation from its quality. Yet, to speak strictly, the intensity of the sensation is not sensed any more than its extent is sensed. We must hold, however strange the conception may be, that it is only the quality which is sensed; while the intensity is an intuition. But so close is the intimacy of the quality and the intensity, that the intensity which is the density even of a point of sensation appears to be and is commonly assumed to be a feature of sensation on a level with its quality. It is the intensity of a quality, whether that quality be blue or sweet or life or motion. In some cases a change of intensity is even confused with one of quality, as sounds of increasing intensity seem to rise also in pitch. Some writers have gone so far as to say (for instance, Mr. Bergson) that intensities really are qualities and every difference of intensity a difference of quality. This seems however not to be in accordance with inspection of experience, which distinguishes quality clearly from intensity.
When we turn to theory we can and must separate the two different integrations of Space-Time which underlie quality and intensity respectively. Quality is the integration of an extensive pattern. The apprehension of it is an enjoyed extensive pattern enjoyed as an extensive whole, but in the sensum what is contemplated is quality. Intensity is the integration of the frequency with which that pattern occupies its space-time, and is apprehended both in the sensum and the mind as such an integration, which in both cases is spatio-temporal and has no quality, though it attaches to a quality. To point this contrast of the two integrations; consider the pattern of a sound vibration which carries the sound in its appropriate pitch, as compared with the amplitude of the vibration which is the intensity of that sound. The greater amplitude means that in the same time there is more of the vibration, or it occupies more space in the same time. The less intense sound leaves part of the space of a greater amplitude unfilled and may thus be brought under the conception of less density. Thus quality is a purely empirical integration; intensity is a categorial one, though of course it has its empirical variations, just as Space or universality has.
Hence, intimate as is the connection between intensity and quality of sensation, so that there is no intensity of a sensum unless there is quality, intensity is and remains purely spatio-temporal. The intensity of sensation belongs with its extent and duration and not with its quality.15
But because intensity belongs even to the minimum extent or duration of a sensum, it is the connecting link between the purely sensory element in the sensum, its quality, and its categorial characters or primary qualities, place, extent, date, duration, to which intensity properly belongs. These characters though revealed to the mind through sensation are apprehended by the intuition which the sensing act contains and which cannot be had apart from the sensing. In other words, the sensing act is a conscious spatio-temporal process, a specialised form of intuition, which in respect of one of its elements, the pattern of response, is aware of the quality of the sensum and performs the sensory function proper; in respect of its other elements is purely intuitive. It is the intuitive elements which give the sensing act its particularity, or individualise it; even as their objects individualise the quality of the sensum. The current statement of psychologists, that sensations possess quality, intensity, extensity, etc., fails to distinguish the different levels to which these two sets of characters belong. It fails also to distinguish between sensing and sensum. For though the sensum possesses quality, blue or sweet, the sensing possesses no such quality but only that of consciousness.16
Extent of sensum.
Leaving intensity let us return to the extent of a sensory object, like a patch of blue, which is an extended multiplicity of sensa. When a sensum is said to have extent it is always such a multiplicity. The extent is extrinsic to the quality of the sensum, which has its own intrinsic extension. It follows that when I see a blue patch I see its blue quality, but I have intuition of its extent. I do not see a blue which possesses an extent but I intuite an extent of space which I see blue. I do not apprehend an extended colour but a coloured extent. The extent is not a property or character either of the mental act of sensing in its sensory character or of its object. It belongs to the act or object of intuition. An important consequence already mentioned more than once follows, not so much for psychology as for the theory of knowledge. If we suppose that our colours are extended and our touches also, we are faced with the problem of correlating the Spaces of vision and touch. They are in that case, as Berkeley rightly held, distinct Spaces, and they do but get connected by custom, though it is difficult to understand how. Now if extent does not belong to colour as such, but colours are seen in their places within an extent, and the like is true of touch, it follows that when we apprehend the same object by sight and touch we are apprehending the same extent, and in the one case seeing its colours and in the other feeling its pressures, and these objects though they do not ultimately occupy, microscopically, the same places do all fall within the same area or volume and macroscopically coincide. There are not two distinct spaces which have to be connected by custom or otherwise, but one space which is the scene of different qualities. What experience does is to correlate colours and touches (and the same thing applies to all the other sense qualities) with one another as belonging to the same space, and this is what our experience of things actually enables us to do.17 Instead of having a variety of different Spaces which we never can make one, except by assuming some Space not given in experience which is the condition of all these various Spaces, our intuitive apprehension of things supplies us with the identical framework of a piece of space, within which the sensible qualities of the things are found. Extent remains a categorial feature of experience, varying of course in empirical differences, and not sensed. It still remains true that what is sensed has its intrinsic spatio-temporal characters, but these are sensed as quality, and not as extended, nor even as having position or place. Hence the necessity of distinguishing the intrinsic extension of the sense-quality as such from the extent (including the place) of the whole sensory experience.
It may be added that with proper changes the same account has to be given of the duration and date of sense experience.
History of ‘extensity.’
This analysis of the connection between sensation and intuition of any space is at variance, though not by any means so sharply as would at first sight appear, with the current doctrine that sensation besides quality and intensity possesses what is called extensity. Were it not or the established use of the word, I should have liked to give the name extensity to the intrinsic extension of a sensum, which is not contemplated as such but as quality, and reserve ‘extension’ for the intuited bigness of a sensory object which arises from the plurality of simple sensa, and is the space in which they are contained. At any rate if the above account be true, sensation as sensory has no extensity as in the commonly accepted doctrine. That doctrine was historically inevitable in view of the failure of the English attempts to derive the percept extension from combinations of touch or colour with motion, and of the resembling theory of Herbart, and in view of the change wrought in the state of the discussion by Lotze's theory of local signs. For Lotze the experience of Space itself was an a priori one: the mind had a native tendency to view its sensory objects as contained in Space. The local signs were needed as indications to the mind so as to assign the various sensory objects to their different places in this Space. His account of them varied in the history of his thought: at first they were mere physical neural processes, apparently noted by the mind unconsciously; but in the end they were described explicitly as sensations, which attended an ordinary sensation in virtue of the place at which it affected the sense-organ of touch or sight. Still, throughout, they remain indications for discriminating place and not experiences of place. Space itself was given to the mind by the mind's own habit. In the justifiable revolt against explaining our experience or any part of it by mental habits, as a method of stating theoretically that we have to accept Space, for instance, as given to us and can offer no further account of it, what could be more natural than to empty this spatiality of experience into the elements of experience itself and declare that our sensations possessed extensity? The doctrine of the extensity of sensations is the inevitable outcome of Lotze's teaching. But the variability with which the local signs have been treated in different expositions of the doctrine of extensity since Lotze is enough to indicate how indistinct the whole doctrine is. Mr. Stumpf dispenses with them altogether. For James they appear to be purely peripheral sense-characters. For Mr. Ward a local sign is the relation of any particular sensation to the presentation-continuum as a whole with its property of extensity. Each presentation has or may have two or more of such local signs, so that each presentation possesses extensity as well as quality.18 Similarly for Mr. Stout the local signs blend together into extensity and a local sign is a differentiation of extensity. These variations in the doctrine, which is much altered from Lotze's, suggest to me that extensity is being all the while regarded as something different from sensation and only connected with it independently; and that is why I said above that my own statement is not so sharply different as it seems. To add to the indistinctness, on some of these theories experience of motion (either kinaesthetic sensation or sensation of external motion) is regarded as an integral constituent of the experience of extension as developed from sensory extensity, and by some (e.g. James) is treated only as a help towards exacter experience.
Place as “partial content” of sensation.
The earlier doctrine of Mr. Stumpf is free from these perplexities, and it will be helpful to touch briefly upon it. For him every sensation possesses four elements or as he calls them “partial contents”19: quality, intensity, time-character, and place. These are “psychological parts” of the sensation. Local signs have no part to play in this analysis. Moreover, he suggests, not of course with the same implications as the present doctrine, that the neural counterpart of the place which is a psychological part of the sensation is the place of the sensory excitement and nothing more.20 What is meant by calling place a partial content of sensation is that quality and place are inseparable from one another, there is no quality which has not extent and no extent without quality. But they are distinct elements and vary independently: the colour of a patch may remain the same though the patch varies in size. At the same time “the quality participates in a certain fashion in the change of the extent,” for the colour diminishes with the extent till, when the extent vanishes, the colour vanishes too.
My only quarrel with this statement is that it fails to mark the difference of mental function in the apprehension of quality and place (and the other partial contents). Both alike are of course contained within the sensation taken as a whole, but they are contained differently. For the purely sensory function is provoked by the quality of the sensum as its stimulus. But the place of the sensum is not a stimulus; the attempt to make it one lay at the bottom of the conception of local signs. Accordingly the place is not a sensory but an intuitive character, and distinct from it to a much greater degree than is suggested by the statement I am considering. The remark quoted that quality in a way participates in the extent proves only that where there is no extent there is no quality. Doubtless it is because quality and place are treated as “contents” of sensation, and not as objects of the sensing, that this distinctness of the sensory and intuitive functions in sensation is minimised.
Remarks on space-perception—Motor sensations.
My inquiry is not primarily psychological and I am concerned only to identify the apprehension of Space and to place it, in its relation with sensation, in a scheme of the modes of mental apprehension corresponding to different levels of existence. Accordingly I am not to discuss those details of how spatial perception is elaborated, which are supplied in such invaluable fulness in recent treatments of the subject.21 But I will allow myself the luxury of commenting upon two matters which fall perhaps outside my scope. The one topic is that of the part played in space-perception by motor or kinaesthetic sensations; they cannot be elements of extension as integral components of it. The case of sensations of motion in things outside us (e.g. a shooting star or a flying bird) is different. Motion is intuited and Space is only the framework of motion, and though we apprehend the motion through sight or touch yet the material derived thus may and must be integral in the direct perception of Space, for it is of that order. But kinaesthetic or motor sensations do not tell us directly of anything outside our bodies which we are contemplating, but only of ourselves, and even then they do not inform us of material motion but of motion within a living thing—vital motion. In exploring with my finger the edge of an object, my finger gives me changing sensations of the touched object and it gives me motion in my body, but the motion does not belong to the body touched. Hence all that such motor sensations can do for space-perception they do not directly but through their correlation with places and extents otherwise known. Their sensa are not ingredients of the extent of place, but they may enable us to refine our apprehension of those places and extents. This would apply to Lotze's attempt to identify the local signs of the eye with sensations of movement or strain in the motor arrangements of the eye. They are not fitted to be local signs, for they tell us of the place of the eye not of the coloured point seen by it. Hence, unless that position is otherwise known, it is difficult to see how this motor sensation could discriminate sensations as belonging to various places in external Space. For the sensations from the thing seen are seen by the mind as external in space to my body, but the motor sensations are felt as in my body. They could not therefore serve as the sign of difference of locality of the sensation.
Local signs as peripheral.
My other remark concerns the attempt to treat local signs as purely peripheral, I mean as tactual or visual in some shape or form. This was Lotze's own view as to the tactual local signs; they were the differences in the feel of touches according to the nature of the underlying structures in different places of the skin. He found no such differences in the retina, and accordingly looked elsewhere for the local signs of the eye. James apparently treats them even in the eye as different feelings at each retinal point. Now it is gravely doubtful whether there is anything like fine enough discrimination supplied in the skin in this way for the purpose, and these different colourings of the touches admit a much simpler interpretation. For the skin not only explores but is explored and is a particularly interesting object of exploration. The different touch experiences from different parts of it serve the same purpose as different colours on a surface, which enable us to see the contours more easily than if the colour were uniform. A body is more easily felt when the surface does not give us uniform touch sensations. Supposing the eyes could see each other, there might be similar variations in the retina, and that they cannot is perhaps the reason why no such differences have been discovered with any certainty.
We must conclude that local signs which are really signs, that is are non-local experiences, cannot do the work required; and that the only local signs which can do the work, namely, central consciousness of the place affected, are not signs at all but are direct consciousness in intuitional form of the place and extent of the external object.
Though I have said nothing of the third dimension, I am assuming that the Space we cognise by intuition is three-dimensional, and the places stimulated in the brain and therefore the places enjoyed in the mind as well as the places in the external thing are places in three-dimensional wholes. Fortunately I am not called upon to raise the question of the optical machinery for apprehension of the third dimension by sight.
Apprehension of life.
The next level of existence above that of the secondary qualities of matter is life, and the quality of life is apprehended in ourselves by the organic and kinaesthetic sensations. In these, as in the special sensations, the act of sensing is distinct from the sensum; the one is an act of consciousness, the other a process of life. The sensum is not sensed through the organic or motor sense as material, which it also is. For this it must be sensed through other sensations. Yet it is as much non-mental as the objects of the special senses. To verify this and at the same time to realise that the object is life and not any mere form of matter, compare in series the sight of an external motion, the sight of one's own moving arm, and the internal sensation of the movement which takes place at the joint. For the visual impression of the moving arm we may even substitute the visual imagination of the movement as taking place at the joints. Now it is the living motion which the motor sensing contemplates; in the other cases it is material motion which is contemplated, though in the one case located in the body, in the other located in the external world, outside the body. Pass from this simpler experience to the organic sensations. My object in the sensation of hunger or thirst is the living process or movement of depletion, such as I observe outside me in purely physiological form in the parched and thirsting condition of the leaves of a plant, which thus lives through its thirst or ‘enjoys’ it, but is not conscious of it, and does not contemplate it as we do our thirst; or the object may be the vital movements implied in suffocation or nausea; or I may have that intensely disagreeable sensum of the laceration of my flesh in a wound, which in its vital quality we speak of as physical pain. In all these instances of motor and organic sensation what we have to do is to separate the consciousness from the object and to recognise that the object-process has the empirical quality of life, which distinguishes it from a primary movement (or from a secondary quality) in matter. The separation is not easy to perform. For we tend to take the hunger as a whole including its conscious character, while at the same time we correlate it with a part of the body in which it is felt. We are the more apt to do so because the unpleasantness of hunger is thought to be eminently psychical, and so hunger tends to be treated as a state of mind. It is no wonder then that we should suppose such a condition to be something mental which is as it were presented to a mind which looks on at it; and that we should go on to apply the same notion to colours and tastes and sounds and regard these as mental in character. Many at least find it difficult not to think, of hunger as a mental affection, arising no doubt from the body.
But the localisation of hunger in the body (however vague) is enough to dispel this misinterpretation and to set the organic and motor sensa on their proper footing. We localise them in our body because we are contemplating an affection of our body, and just for the same reason we localise our touches or pressures not only in the object touched but in the skin which is touched where the pressure also occurs, for within limits the skin and the surface of the thing touched are one and the same surface. For the opposite reason we do not localise our sensa of colour in the eye, but in the thing seen, and we are said in misleading and unjustifiable phrase to project our visual sensations (unjustifiable I mean if we really imply that we first feel the sensa in ourselves and then project them beyond us). We only know in fact that our eyes are concerned in seeing colours of things from the sensations of movements in the eyes in regarding the thing, or from the experience that we see or do not see according as the eyes are in the open or shut position, which is revealed by sensations of position. Rightly understood the organic and motor sensations confirm the general analysis of sensation into an enjoyment compresent with its non-mental object. Begin with a superficial regard for them and the theory of the special sensations also is corrupted.
The same considerations as we have urged in the preceding chapter enable us to discriminate the consciousness of pleasure and painfulness from these affections themselves, and lead us to believe that pleasure and pain are data not of the mental but of the vital order, of the same class as the organic sensations, but whose precise nature it is not at present possible to state.22
A special interest attaches to the sense of resistance, which is one form of motor sensation. There, as we just saw not only have we the consciousness of the vital process of strain but of something which is not merely touched but has the quality we speak of as resistance, that is of materiality. It is the consciousness of a vital process opposed by something material, not of matter as opposed by matter, such as we have when we contemplate the shock of two billiard balls. This last we understand only when we have arrived at the experience of both balls as material, in the way before described. But our understanding is helped in the matter by the experience of resistance from one part of our own bodies to another part of the same body. When I press my finger against the ball of my thumb, besides the awareness of my thumb as resistant and material, I am aware of it as itself the seat of a strain and vital. Each of the two parts of the body is experienced as at once resisted and resistant, each suffers and offers resistance. There are two objects each of which as resistant is material and suffers resistance as vital. It is in consequence of such an experience that when we press a merely material object we describe our sense of strain as the sense of resistance on our part to matter. But this experience helps us also to understand (and this is its chief significance) material inertia as the resistant act or activity of a body which is not vital, and the mutual relation between two material foreign bodies as resistance between them.
Apprehension of foreign life.
But our contemplation of vitality is in the first instance of our own. How do we apprehend life in the tree outside our body? For we perceive other living things only in their material qualities and their motions and other primary qualities. Their motions are complex and may be self-initiated, but examination shows them to be dependent like everything else, including ourselves, upon their surroundings. Their motions are set going partly by internal stimuli; but they act within their external circumstances. What distinguishes them from a machine is their vitality, which includes plasticity. In one respect they are machines of a certain high order, just as in that respect our bodies are, when we exclude the vitality which is in the same place as our body and is thus possessed by it. How then are we aware of the tree's life? Not certainly by projecting our life into the tree, for I may certainly see the tree to be alive without being sensible of my own life. I am sensible of myself in being conscious of the tree and of its life, and do not refer to my own life. When we discussed the consciousness we have of other minds we saw how impossible the conception of projection was in that case, and how we could not be aware of other minds even by analogy with our own. For we enjoy only ourselves, and that there could be something else which enjoyed itself was a new discovery which depended on a special sort of experience.
But in the case of life outside ourselves, though there is no projection, there is something which may be called analogy. For our life is not enjoyed by us, but it is contemplated. We are aware through appropriate sensations of something non-mental which is life. We do not become aware of it as limited to us and our bodies, though as a matter of fact we contemplate it then only in connection with our bodies. Accordingly, a set of external motions of the same kind as our own is apprehended as alive. If this be called analogy I am content, but it is the same process as we use in extending throughout our experience a quality learned in connection with one example of a kind of things to another example. I contemplate life in a body which is my own; and I contemplate also in that body the motions or behaviour which are apprehended as vital because they are in the same place as the vital motions and are identical with them. In other words, what I apprehend as external material behaviour is also apprehended as alive. Just because the vitality in that body of mine is contemplated and qualifies the same body apprehended as material with its primary and secondary qualities, I can qualify a foreign body which behaves in the same sort of way as alive. I have touched a piece of ice and found it cold. I see another piece of ice and I qualify it as cold without having touched it. I see the plant alive just as I see the ice cold. The only difference is that there is only one body in the case of which I make direct acquaintance with life, while there are many pieces of ice from which to learn the connection of cold with the colour and shape. Such an instance of the ordinary process of extending our experience from one thing to another, subject to verification, is hardly to be dignified with the grave name of analogy. Yet the process is a less explicit form of analogy. The assurance we have of other minds was not derived from analogy at all but demanded a special experience. The reason is that mind is not contemplated but enjoyed, and enjoyment is as such unique to the individual and cannot be shared with others. But I do not experience life as mine or peculiar to me; and life is not enjoyed but contemplated, and consequently, without any fresh revelation, is extended to other bodies of a certain sort. This being granted, analogy in the stricter sense has also its place in the interpretation of foreign life as it has with foreign mind. The details of our own life may be used to interpret more finely and exactly, whether in the way of extension or limitation or discrimination, the bodily foundations of life which we observe outside ourselves. We may better understand the thirst and hunger of the plant, and learn being, to a certain range of external objects, such as the air or things in contact with the body. External things act upon the animal's body without being revealed to consciousness. Physiological reflexes may be even more efficient for having no conscious object to which they are correlated; i.e. if they only enter into consciousness so far as the motor response itself is sensed and the animal knows what state of his body is the outcome. Thus a conscious being may do without external sensibility, provided it is aware consciously of its own bodily self.
But though the order in time of the senses does not necessarily agree with the order in time of their sensa, categorial cognition, or intuition, precedes all sensation, not as an isolated form of apprehension, but in the sense that it is contained in sensation and masked by it.
The above conception of the apprehension of locality as distinct from sensation and as belonging primarily to the place of the nervous system which is excited by the sensation said to be ‘referred’ to the place in question is, it must be admitted, one of some difficulty. It is in accordance with the general scheme elaborated in this work, but it may be suspected of being nothing more than a mere hypothesis invented to this end, and of conflicting with known facts of psychology, and more particularly of neurology. Some further commentary and explanation are therefore added in an appendix.
Its conflict with the current theory of local signature and of the movement-experiences required to determine exact locality, apartness of two touches or colours, shape, size, etc., is not so serious a difficulty and has been met in the text. The whole notion of extensity and local signature as characters of sensation is obscure in the extreme, and is in fact invented rather upon psychological grounds than on any distinct neurological evidence; while the doctrine that definite localisation and shape require also movement sensations is for the reasons given above still more debateable. In its general feature of separating spatial experience from sensation of qualities it is in agreement with the doctrine of Dr. H. Head and his collaborators, for whom localisation of touches and also discrimination of co-existent touches are conveyed by impulses distinct from those of touch or movement.
On the other hand, the agreement is at first sight only general and limited to the proposition that spatial experience and sensory experience are distinguishable and separate. Moreover, the above theory seems at first sight difficult to reconcile with some of the facts established in the latter remarkable set of experimental investigations. They are reported in Brain, vols, xxix., xxxi., xxxiv. (1906–12), and recently xli. (1918).
By localisation is meant ability to determine the place on the body of a spot touched, whether by naming it or pointing to it with the finger, or pointing to the corresponding place on a picture of the limb, or, better still, on the same limb of another person. Discrimination is the ability to distinguish two simultaneous touches, or, in Mr. Stout's language, to recognise their apartness. There are separate impulses for these two processes, which are also distinct from touch impulses and from those of posture and movement. But according to these researches, which are founded on a number of cases of nervous lesions in the spinal cord the optic thalamus, and the cerebral cortex, these various impulses and those of heat and cold and pain become variously regrouped in their course through the spinal cord and above, before they cross to the other side of the body. Pain, heat, and cold impulses cross in the spinal cord first, touch impulses later. Localisation and discrimination remain at first grouped with touch impulses. The localisation impulses remain grouped with touches (whether deep touches or light ‘epicritical’ ones) below the spinal level, but in the brain-stem they may be separated. On the other hand, tactile discrimination and posture impulses do not cross at the spinal level nor until they reach the medulla oblongata. Lesions of the optic thalamus show that localisation or spot-finding is separate from touch, and lesions of the cerebral cortex show that neither localisation nor discrimination is dependent on touch, nor again upon posture, the sense for which is often gravely disturbed in lesions of the cortex. Finally, in the last of these researches,23 the result is arrived at roundly that the optic thalamus is the special seat of sensation so far as its mere quality is concerned, while the special function of the cortex is the apprehension, not of the quality of sensations but of their differences of intensity, the likeness and difference, the weight, size, shape of things, or in general the spatial aspects of sensation.
The great importance of these inquiries for psychology is the distinction they establish on empirical evidence between tactual (or other cutaneous) sensibility and the apprehension of the precise spatial and temporal characters of touch as requiring a separate machinery. The meaning of them is not, as I take it, that these are two distinct groups of sensations brought to consciousness, as sensations are commonly understood to be, by separate neural paths; but rather that, in the language used more particularly in the last of these researches, place and quality are distinct aspects of the whole sensory process, the mere tactile aspect or function being specially provided for in the thalamus, the spatial aspects more specially provided for in the cortex. Touch sensation belongs to both, but the cortex is the instrument which performs the function of discrimination of all sorts, direct spatial discrimination of touches, that of intensities, and the like. So understood, the generalisation is not open to the objections brought against it (e.g. by Mr. Stout, Manual, p. 245) of running counter to ordinary ideas of sense-stimulation. No theory is offered (as in the speculation of my text) as to the nature of the difference, but only as to the physiological basis of it. I venture to think that my speculation as to the nature of the distinction is not incompatible with these results, but merely gives them a different speculative reading. Holding that spatial intuitions are elicited through touch sensations by the excitement of the places where they occur, I should have to say that while any touch sensation gives an intuition of place, it is only in the cortex that the local touch excitement is accurately differentiated in the reaction which it gives according to its locality.
There remains the initial and fundamental difference that Mr. Head and his colleagues treat quality and spatial characters as being characters of the sensation as a whole, whereas for me quality and place are objects and the sensing process is purely spatio-temporal and has no quality but that of being conscious. This question is of course not raised in these researches. It makes a great difference in the end. For in the first place the view of the text dispenses with the notion that the place of a stimulus is a stimulus in the same sense as its pressure or colour; secondly, it enables us to understand how a touch and a colour can belong to the same place, while otherwise we are beset still with the old problem of how to correlate the place which is an aspect of touch sensation with the place which is an aspect of colour sensation; and thirdly, it does away with the fundamental difficulty of how sensations can be projected and referred to the external world, whereas if place is a character of sensation itself, it does not help us in referring a touch or colour outside the mind.
On the other hand, the speculation of the text labours under objections which at first sight seem difficult to overcome in view of the facts established in these researches. It would seem to imply that when there is a touch there is not only intuition of its and other discriminative characters, but an infallible one. Yet with cerebral lesion touch may be preserved, while localisation and discrimination are injured or destroyed. Something has Keen said briefly to anticipate this objection, and more wilt be id in the next chapter, to the effect that intuition goes no further than sensation gives it warrant, and suffers from the disabilities which attend the sensory, or qualitative, function proper. I will therefore refer briefly to a few of these points. Take localisation or spot-finding on the body. To be aware of the place of a touch does not mean to localise it in its place in the body. That, as is pointed out (Brain, xxxiv. p. 187) implies a body schema, which is a touch schema. Now the monad lifted up into intuition through sensation has not consciousness of its own right in virtue of which it should localise the touched place in the spatial schema as identified with the body. To do this it would need a touch schema, and it is limited to its own touch. Discrimination, again, implies an unexcited interval. But if the touches are indistinct in the sense described, their distinctness of place will be similarly affected for the monads of the two touches. Another striking observation is the radiation or diffusion of sensations of heat and cold and pain in the protopathic state, when there is no epicritical sensibility to control it; and besides their diffusion, their reference to remote parts of the skin. The diffusion means, I imagine, that the sensations are blurred in their reaction, and thus the intuitions of their places in the brain indistinct. This is the case also with the organic sensations to which protopathic sensations are allied. The misreference of the sensations I cannot explain, but it is analogous to the tenderness felt in allied parts of the skin from internal pains, as Mr. Head himself points out, and appears to be connected with the character of the reaction. Guarded in fact as I have guarded the statement of the text, it appears thus to say the same thing as Mr. Head's doctrine in other words. The office of sensation of touch or colour is to give us touch and colour and not place. But to have these sensa distinct is to have distinct intuition of their places; to have them indistinct is to have failure of the intuition. The conclusion is that distinctness of mere sensory quality is ultimately spatio-temporal. What the text does is thus merely to offer a speculative theory of the more elementary nature of the intuitive characters. Finally, having regard to the conclusion arrived at in this chapter that intensity is spatio-temporal and not qualitative, cannot help pointing out the importance of the observations which seem to show that difference of intensity of sensations is an affair of the cortex and therefore on a level with space-difference, while in the thalamus, where spatial sensitiveness is undeveloped and primitive, the reaction is of the ‘all or none’ type.
The question may still be asked how, if Space and Time are the simplest and most fundamental characters of the world, the apprehension of them should be entrusted to the latest and most highly developed part of the nervous system. A similar question in the reverse form, met us at the end of the chapter, how the organic sensations which apprehend a higher level of existence, life, than the special senses, should be earlier and more primitive in development. The answer is that spatial character, as I understand these inquiries, does belong to sensory process below the cortical level, but it is vague and undifferentiated; and so also does intensity. And, secondly, the vaguer, more extensive reactions are suitable to that stage of life, and the precise apprehension of Space and Time made possible by the cortex is appropriate to the higher type of mental life.
I am following Kant's use of the word Anschauung, as distinguished from sensation (Empfindung) and perception (Wahrnehmung), without the implications of Kant's subjective doctrine of Space and Time. Unfortunately the word intuition suggests direct or self-evident apprehension as contrasted with indirect. It has no such implication here. Intuition is no more direct than sensation and thought. All our apprehensions bring us face to face with their objects.
Λογισμω τινι νοθω, 52 b.
This problem is discussed in ch. vii. pp. 192 ff.
For further discussion of localisation see Supplementary Note at the end of the chapter.
Above, ch. i. A, p. 25.
See above, Bk. II. ch. vi. A, vol. i. pp. 276 ff.
Pictorially this transition of one movement into another is represented by depicting two stages of the movement separately, as in Michael Angelo's representation of God's creation of the sun (another observation which I owe to the late Hermann Grimm).
See also Bk. I. ch. iii.
See before, Introduction, vol. i. p. 28.
For the above see Mind, vol. xxi. N. S., 1912, “On relations, etc.” § 7, pp. 121 ff.
See below, ch. vi. p. 175.
See above, Bk. II. ch. vi. A, vol. i. p. 275.
Above, ch. v. p. 133. Brentano, Untersuchungen, p. 14.
When the whole hand or arm is plunged in hot water the water seems hotter than when only a finger or a finger-tip is immersed. This fact is of a different kind from that in the text. There the intensity or brightness is lowered by leaving unexcited places. Here we have a larger extent of the same density of stippling confused with a greater intensity. The fact is a further illustration of the truth that intensity is dependent on an extensive condition. The larger extent of the heat besides being felt as larger appears to be taken in as a whole and to be equated with a greater density of the heat. There are other illusions which are perhaps cognate. To the touch a line of points feels shorter than a continuous line of the same length. Oddly enough this is an‘illusion’ opposite to that of vision, for as is well known a line of points looks longer than a continuous line of the same length, at any rate within certain limits of length.
There is therefore no extravagance in the suggestion sometimes made (as by Messrs. Münsterberg and Brentano) that the intensity of different orders (or modalities) of sensation, e.g. touch and sound, may be compared and equated.
I add a note on order. Both the sensum and the sensing possess order in respect of any of its characters. The order in quality of the sensum is its place in the series of qualities, e.g. if it is a sound, in the series of qualities called pitches. The corresponding order in the sensing is that of the patterns of response. These are without sound quality and it is in respect of the sensings of sounds, not of the sensa themselves, that Mr. Watt's proposition is true, that pitches are not differences of quality but of order. Thus the order of quality in sensation belongs to the sensory side of sensation, not to the intuitive side. (This repeats a note on a previous page, vol. i. p. 265.)
I am once more neglecting the variation of spaces in our sensible experience.
See Art. Encycl. Brit. ed. ix. p. 54. Psychological Principles, pp.
Ueber den psychologischen Ursprung der Raumvorstellung. Leipzig, 1873, pp. 106 ff.
Pp. 149 ff.
Cp. Mr. Stout's chapters in Manual, ed. 3, Bk. iii. pt. ii. chs. iii., iv.
There is a point of difference between the organic and kinaesthetic on one hand and the special senses on the other which has been already mentioned in connection with the subject of remembering emotions,1 but which may be repeated shortly here because it has importance for the theory of knowledge as well as for psychology. The sensum of the special senses is in general external to the body; but that of the organic and motor senses is the living body itself, of which body the neural equivalent of the consciousness of the sensa is itself a part. The consequence is that ideas of these vital sensa tend to become sensational, that is hallucinatory. Except in certain well-attested cases this is not true of the special senses. We do not by imagining a sensory quality make it present to ourselves in sensation. Who can hold a fire in his hand by thinking of the frosty Caucasus? But a motor or organic idea tends of its own motor character to stir up the organs themselves, which are the source of the experience and so to produce the conditions of sensation. Even with the special senses we try, if the object present to sense is agreeable, to get more of it, but this is not possible in idea. What is unusual here is normal with the vital sensibility; the idea repeats itself in sensory form, because its object is the body itself.
1 Bk. II. ch. iv. vol. i. p. 131 note.
Which I have made acquaintance with while this work is in course of printing.