Essays Towards a Theory of Knowledge

by Alexander Philip

We do not propose now to devote any time to the work of showing that sensations from their very nature could never become the instruments of Knowledge. We propose rather to turn to the principal ideas of the external world which are the common equipment of the Mind in order to ascertain whether in point of fact they are derived from Sensation.

Of course to some extent the answer depends on what we mean by Sensation. If by that term we intend our whole Experience of the external, then of course it necessarily follows—or, at least, we admit—that our Knowledge of the external must be thence derived. But such a use of the term is loose, misleading, and infrequent. The only safe course is to confine the term Sensation to the immediate data of the five senses—touch, sight, hearing, smell, and taste, with probably the addition of muscular and other internal feelings. It is in this sense that the word is usually employed, and has been employed by the Sensationalist School themselves.

Now we might perhaps begin by taking the idea of Time as a concept constantly employed in Discourse, but of which it would be absurd to suggest that it is supplied to us by Sensation. It might, however, be urged in reply that the idea of Time is not derived from the external world at all, but is furnished to us directly by the operations of the Mind, and that therefore its intellectual origin need not involve any exception to the general rule that the materials of our Knowledge of the world are furnished by Sensation alone. Without, therefore, entering upon any discussion of the interesting question as to what is the real nature of Time, we shall pass to the idea of Space.

Mach, the writer whom we have already quoted, in his essay on Space and Geometry speaks constantly and freely of sensations of Space, and as there can be no denial of the fact that Space is a constituent of the external world, it would seem to follow that those who hold Sensation to be the only source of our Knowledge must be obliged to affirm the possibility of sensations of Space. Mach indeed claims to distinguish physiological Space, geometrical Space, visual Space, tactual Space as all different and yet apparently harmoniously blended in our Experience. He is, however, sadly wanting in clearness of statement. He never tells us when and where exactly we do have a sensation of Space. In truth he never gets behind the postulate of an all-enveloping tridimensional world; so that he throughout assumes Space as a datum, and his inquiry is an effort to rediscover Space where he has already placed it.

Let us, however, consider for a moment what can be meant by a sensation of Space. Does it not look very like a contradiction in terms? Pure Space, if it means anything, means absolute material emptiness and vacuity. How, then, by any possibility can it give rise to a sensation? What sensory organ can it be conceived as affecting? How and in what way can it be felt?

The truth is the idea of Space is essentially negative. It represents absence of physical obstruction of every kind. No doubt, we may describe it positively as a possibility of free movement, and such a description is at once true and important. Yet even it involves a negative. The term "free" is in reality, though not in form, a negative term and means "unconstrained." And the reason why such a term is necessarily negative is to be found in the fact that a state of dynamic constraint is the essential condition under which we enter upon our organic existence. Freedom is a negation of the Actual. Absolute freedom is a condition only theoretically possible, and is essentially the negation of the state of restraint in which our life is maintained.

But the definition last quoted is nevertheless valuable because it clearly shows what really is the origin of the idea of Space. It proves that the idea of Space is a representation of one condition of our Activity. It is because the primary work of Thought is to represent the forms of our dynamic Activity that we find the idea of Space so necessary and fundamental.

But it will perhaps be argued that our ordinary sensations carry with them a spatial meaning and implication, and that indirectly, therefore, our sensations do supply us with the idea of Space. It will readily be agreed that if this is so of any sensations it is pre-eminently true of the sensations of vision and touch. Indeed, it will perhaps not be disputed that the ordinary vident man derives from the sensations of vision his most common spatial conceptions. We propose, therefore, to inquire very briefly how the character of spatial extension becomes associated with the data of Vision.

The objects of Vision appear to be displayed before us in immense multitude, each distinct from its adjacent neighbour, yet all inter-related as parts of one single whole—the presentation thus constituting what is called Extensity.