16. The real source of these embarrassments in Locke’s theory, it must be noted, lies in the attempt to make the individual consciousness give an answer to its interrogator as to the beginning of knowledge. The individual looking back on an imaginary earliest experience pronounces himself in that experience to have been simply sensitive and passive. But by this he means consciously sensitive _of something_ and consciously passive _in relation to something_. That is, he supposes the primitive experience to have involved consciousness of a self on the one hand and of a thing on the other, as well as of a relation between the two. In the ‘idea of sensation’ as Locke conceived it, such a consciousness is clearly implied, notwithstanding his confusion of terms. The idea is a perception, or consciousness _of a thing_, as opposed to a sensation proper or affection of the bodily organs. Of the perception, again, there is an idea, _i.e._ a consciousness by the man, in the perception, of himself in negative relation to the thing that is his object, and this consciousness (if we would make Locke consistent in excluding an unperceived perception) must be taken to go along with the perceptive act itself. No less than this indeed can be involved in any act that is to be the beginning of knowledge at all. It is the minimum of possible thought or intelligence, and the thinking man, looking for this beginning in the earliest experience of the individual human animal, must needs find it there. But this means no less than that he is finding there already the conceptions of substance and relation. Hence a double contradiction: firstly, a contradiction between the primariness of self-conscious cognisance of a thing, as the beginning of possible knowledge, on the one hand, and the primariness of animal sensation in the history of the individual man on the other; secondly, a contradiction between the primariness in knowledge of the ideas of substance and relation, and the seemingly gradual attainment of those ‘abstractions’ by the individual intellect. The former of these contradictions is blurred by Locke in the two main confusions which we have so far noticed: _(a)_ the confusion between sensation proper and perception, which is covered under the phrase ‘idea of sensation;’ a phrase which, if sensation means the first act of intelligence, is pleonastic, and if it means the ‘motion of the outward parts continued to the brain,’ is unmeaning; and _(b)_ the confusion between the physical affection of the brain and the act of the self-conscious subject, covered under the equivocal metaphor of impression. The latter contradiction, that concerning the ideas of substance and relation, has to be further considered. How this contradiction is disguised.