Quite apart, then, from the question as to whether Descartes’ doctrine of representative perception rests on a correct interpretation of the teaching of the natural sciences--Kant was ultimately led to reject the doctrine--it is obvious that the main epistemological problem, _i.e._ the problem how awareness is possible, and in what it consists, has so far not so much as even been raised. Descartes and his successors virtually assume that consciousness is an ultimate, unanalysable form of awareness, and that all that can reasonably be demanded of the philosopher is that he explain what objects are actually presented to it, and under what conditions their presentation can occur. On Descartes’ view they are conditioned by antecedent physical and physiological processes; according to Berkeley they are due to the creative activity of a Divine Being; according to Hume nothing whatsoever can be determined as to their originating causes. But all three fail to recognise that even granting the objects to be of the character asserted, namely, mental, the further problem still remains for consideration, how they come to be consciously apprehended, and in what such awareness consists. Certain interpretations of the nature of the knowing process are, of course, to be found in the writings of Descartes and his successors. But they are so much a matter of unexamined presupposition that they never receive exact formulation, and alternate with one another in quite a haphazard fashion. We may consider three typical views. 1. There is, Descartes frequently seems to imply--the same assumption is evident throughout Locke’s _Essay_--a self that stands behind all mental states, observing and apprehending them. Consciousness is the power which this self has of contemplating both itself and its ideas. Obviously this is a mere ignoring of the issue. If we assume an observer, we _ipso facto_ postulate a process of observation, but we have not explained or even defined it. 2. There is also in Descartes a second, very different, view of consciousness, namely, as a diaphanous medium analogous to light. Just as light is popularly conceived as revealing the objects upon which it falls, so consciousness is regarded as revealing to us our inner states. This view of consciousness, for reasons which I shall indicate shortly, is entirely inadequate to the facts for which we have to account. It is no more tenable than the corresponding view of light.