Categories are forms of cognitive consciousness; they are universal principles or relations presupposed either in all cognition or in all cognition of a certain kind. It was a main part of the work of Kant to exhibit the categories involved in our knowledge of the external world, such as Quantity, extensive and intensive, Causality, Substance, etc. These are the ultimate relations between the specific contents of our experience, and constitute the forms of synthesis which give unity to that experience.

Now in a rudimentary way these forms of synthesis, or some of them, appear at the level of perceptual activity. There are five which require special treatment,— External or Physical Reality, Space, Time, Causality, and what for want of a more familiar word we must call Thinghood. The first three of these will receive consideration in chapters especially devoted to them.* Of course such forms are not distinctly apprehended by the perceptual consciousness in abstraction from the concrete matter of experience to which they give order and unity. But neither are the categories of human thought distinctly apprehended, as such, until a comparatively advanced stage of development is reached. Even then, they are only imperfectly and incompletely detached from the more concrete matter in which they are, so to speak, embedded. If this were not so, Logic and Theory of Knowledge would have nothing to do.

* We shall deal with Causality and Thinghood in the present chapter.

J. F. Ferrier puts the case extremely well. "Men reasoned generation after generation long before they knew a single dialectical rule, or had any notion of the construction of the syllogism. The principles of logic were operative in every ratiocination, yet the reasoner was incognisant of their influence until Aristotle anatomised the process."* Ferrier further illustrates by referring to other constitutive forms which have only been gradually disengaged by reflective analysis from their specific embodiment. "It is," he says, "always very late in the day before the seminal principles of speech are detected and explained. Indeed, the language which owed to them both birth and growth may have ceased to be a living tongue before these, the regulating elements of its formation, come to light and are embodied in written grammar. That most elementary species of instruction which we familiarly term the A, B, C, had no express or articulate existence in the minds or on the lips of men, until thousands of years after the invention and employment of language; yet these, the vital constituents of all speech, were there from the beginning."+

* Institutes of Metaphysic, p. 15.            + Ibid., p. 14.

It is only in this sense that we suppose the categories of perceptual thought to exist for the percipient. They exist for him as the alphabet existed before its discovery. Now in this sense Causality is undoubtedly a category of perceptual consciousness. Perceptual process is directed towards practical ends; and it learns by experience how to attain these ends. Actions which prove ineffective are gradually discontinued, and actions which prove effective are maintained and repeated. Consider the dog or cat in Mr. Thorndike's experiment previously quoted.* The animal is confined in a box, with food outside. It can only escape by turning a wooden button, pulling a loop, or pressing down a lever. It struggles to escape in all kinds of ways, squeezing and biting and clawing. Ineffective modes of action are discontinued and give place to others, which in their turn are discontinued if they prove fruitless. If in this way the animal does accidentally work the mechanism, it is likely to do it sooner when again put into the box. Thus in repeated experiments "all the squeezings and bitings and clawings which do not hit the vital point of the mechanism . . . get stamped out, while the particular impulse which made the successful clawing or biting, gets stamped in," until it alone is executed. This gradual adaptation of means for the attainment of ends involves in a rudimentary way the category of Causality. It involves the distinction between efficiency and inefficiency. It is the startingpoint and presupposition of all subsequent developments of thought which proceed according to this category.

* See p. 259 ff.

But we must notice the essential difference which separates the merely perceptual category from that of ideational and conceptual thought. The perceptual category is always purely and immediately practical in its operation. It is a constitutive form of thought only because it is a constitutive form of action. The question Why? has no existence for the merely perceptual consciousness. It does not and can not inquire how it is that a certain cause produces a certain effect. It does not and can not endeavour to explain, to analyse conditions so as to present a cause as also a reason. It does not compare different modes of procedure or different groups of circumstances, so as to contradistinguish the precise points in which they agree from those in which they disagree, and in this way to explain why a certain result should follow in one case and a different result in another case. Causality in this sense can only exist for the ideational consciousness, and the development of the ideational consciousness in this direction is a development of conceptual thinking, — of generalisation.

What corresponds on the perceptual level to Kant's category of Substance is a category which I can only describe as that of Thinghood. In considering it we must lay aside the notions which connect themselves with the scientific view of substance as a stuff or material which persists and passes into various forms and combinations without increase or diminution of quantity. We must rather think of that unity and identity, and independence, which characterises what in ordinary practical life we call a "thing." A thing is a portion of matter which is apprehended as identical with itself and distinct from all else under its varying aspects and throughout its varying changes of state.