Page images
PDF
EPUB

ternal world which has been at the back of the scientific mind since the time of Descartes and Locke. In its original form this view was a mass of inconsistencies, since it was naïvely realistic for our perception of shape, size, and position, and held a causal theory for our perception of colour, temperature, etc. This combination of theories proved to be inconsistent with the inextricable entanglement of the two kinds of qualities, which we actually find. Moreover, the naïvely realistic part of it proved untenable in face of the variations of visual shape and size, which are obvious when we view what is regarded as a single unchanged physical object from various positions.

Thus the only hope for the scientific view was to restate it in a completely causal form. A serious difficulty at once arose. The causal part of the old view presupposed the naïvely realistic part. When we were told that motions within a circular contour at a certain place in space caused sensations of colour and temperature "in us," we understood this, because we thought that we literally saw and felt this contour in this place. But, as soon as the theory is made completely causal, both spatial and non-spatial attributes belong primarily to the effect produced "in us" by something else. It then becomes difficult to see that we have any better right to regard this cause as literally endowed with shape, size, and position, than as literally endowed with colour and temperature. Yet the scientific theories about the causation of our sensations of colour, temperature, etc., are stated in terms which seem to lose all meaning unless the causes of these sensations literally have shapes, sizes, and positions. The Critical Scientific Theory, as stated by us, has been an attempt to meet these difficulties, to reformulate the distinction between primary and secondary qualities, and to estimate the amount of value which this distinction can justly claim.

I think that the Critical Scientific Theory is internally consistent, so far as it goes; but I certainly do not believe that it is ultimately satisfactory. In the first

place, it continues to use a number of phrases whose meanings are no longer obvious when we have given up the notion that we literally sense parts of the surfaces of physical objects. It still talks of pennies being "round," of a number of different people at "the same time" and the same person at "different times" all perceiving "the same penny" from "different places." We must reinterpret all these phrases in terms of our sensa and their relations before we can hope to get a consistent theory. I shall try my hand at this very difficult job in the next three chapters.

[ocr errors]

Secondly, our theory uses the phrase that processes in external physical objects and our bodies "jointly) produce in us the sensa by which we become aware of them. The phrase in inverted commas covers a multitude of problems. Do physical processes create sensa out of nothing? Or do they just cause us to sense now one and now another selection out of a mass of already existing sensa? And, on either alternative, what is the status of sensa once they have come into existence? Do they just exist alongside of physical objects? Do they ever interact with each other or produce effects on the physical world? Or are they, in some Pickwickian sense, parts of physical objects? With some of these problems I shall try to deal in my last chapter.

The following additional works may be consulted with advantage:

B. A. W. RUSSELL, Lectures on the External World, Lects.
III. and IV.

Analysis of Mind, Lects. V. and VII.

G. F. STOUT, Manual of Psychology, Bk. III. Part II. Cap.
I., and Bk. II. Cap. I.
Proceedings of the Aristotelian Society, 1913.

"

[ocr errors]

J. LAIRD, Problems of the Self, Cap. III.

S. ALEXANDER, Space, Time, and Deity, Vol. II. p. 124, et seq.; p. 170, et seq.

G. E. MOORE, Philosophical Studies.

BERKELEY, Principles of Human Knowledge.
DESCARTES, Meditations.

CHAPTER IX

"Nam si colores et soni in ipso Objecto essent, separari ab illis non possent. Separantur autem, ut manifestum in reflexionibus visibilium per specula, et audibilium per loca montana. Scimus autem corpus quod videmus in uno tantum loco esse, sed apparentias in plurimis."

(HOBBES, Leviathan, Part I. Cap. I.)

The Positions and Shapes of Sensa and of
Physical Objects

We have now to dig beneath the assumptions that are tacitly made by the Critical Scientific Theory, and to discover their precise meaning and value. In expounding it we talked of a number of people all "looking at the same penny." We assumed that there is a certain place "seen" by all the observers, and that in this place there is a round physical object. We have now to ask what is meant by a common place; what is meant by a physical object occupying that place; and what is meant by calling that object round. We shall find that all these questions, which seem so childishly simple, present great difficulties, and can only be answered in highly Pickwickian senses. They seem easy, because we habitually confine ourselves to cases, which are indeed of frequent occurrence, and are of practical interest, but which really owe their simplicity to the existence of specially simple conditions. These conditions are not always fulfilled, and then difficulties arise. This happens, for instance, with mirror images which turn up in places where nothing relevant is going on. As a rule, we simply ignore these "wild" sensa; but we shall find that the only way to deal fairly with all the facts is to base our theory on them, and to

regard "tame tame" sensa as owing their tameness to the fulfilment of certain special simplifying conditions.

In dealing with our present problem we shall not only be learning something more about the concept of Matter and its appearances; we shall also be carrying the theory of Space a step further. In Chapter I we simply took the common-sense notion of a single allcontaining Space for granted; we have now to consider the exact cash value of that conception.

If we want to discover the meaning of the statement that we all see a certain physical object in a certain place, we must start from the spatial characteristics of our visual sensa. Unfortunately, there is a good deal of disagreement as to what these actually are. Thus we are often told that we do not "see" distance or solidity; and this is undoubtedly meant to mean that distance and solidity are not characteristics of visual sensa, as shape and size are. This seems to me to be a mistake, and the whole matter has become so much confused that our first duty is to try to clear it up. This will be rather a long process.

When

Spatial Characteristics of the Visual Field. ever I open my eyes I am aware of a coloured field of view, which I will call a "visual field." It is admitted that this is spread out and internally differentiated into patches of various shapes and colours. These are at once joined and separated by a background, which also has colour. The middle part of this field is the most distinct. If I turn my head a little, the field changes slightly. What is now in the middle and most distinct differs from what was in the middle of my former field. But it is extremely like something that was slightly to one side of the former field and was slightly indistinct. Conversely, what is slightly to one side of the present field is very much like what was in the middle of the former field and had there maximum distinctness. The process of turning one's head is, of course, associated

with certain kinæsthetic sensations, which last longer and grow more intense the more the head is turned.

(a) Visual Motion.-So much, I suppose, is admitted by everyone. I now want to call attention to certain facts that have an important bearing on our present problem, and are not so commonly noticed. As a rule, we see objects through a practically homogeneous medium, viz., air, in which they and we are immersed. Under these conditions the slight turning of the head only produces those changes in centrality and distinctness that we have noticed, combined, of course, with the loss of certain features which were on the extreme edge of the first field and the gain of others on the opposite extreme edge of the second. So long as the medium is homogeneous, the turning of the head does not affect the visual sensa with sensible movement. If, on the other hand, we are looking through a bad bit of window glass, or through any optical instrument imperfectly focused, the sensa in the field do visibly move as we turn our heads. What I call "sensible movement" is as distinct and irreducible a character of certain sensa at certain times as colour or shape. We notice then that, under normal conditions of sight, the sensa in our visual field may be unaffected with sensible movement, though we turn our heads; but, as soon as the conditions become unusual, a turn of the head affects all the sensa of the field with sensible movement.

Again, some of the sensa in a field may be affected with sensible movement though I keep my head still. As I write, I am sitting at an open window in Trinity, and looking out at the opposite side of Nevile's Court. All the points that I have mentioned are illustrated in my present visual field. I can turn my head without the visual appearances of the opposite windows being affected with sensible movement. If I look through the shut window, which is at the side of my open one, and is made of rather irregular glass, I find that I cannot turn my head without the visual appearance of the

« PreviousContinue »