by way of caution; you must not expect to be able to verify the fact of sensation and the fact of thought apart from each other; you must not expect to be able to study the phenomenon of sensation by itself and prescinded from all thought. That is impossible: because, in the very act of studying the sensation, you must think it; so that it is impossible to lay hold of it by itself. The two cannot be separated in such a way as may enable you to report upon sensation without taking thought into account as well. But still, although the two must be taken together, this need not prevent us from obtaining a distinct conception of each, or from perceiving that the one element is quite different from the other, that each is, indeed, the opposite of the other.
22. Having thus put you on your guard against encouraging an expectation which cannot possibly be fulfilled, I go on to stimulate your own reflections with the view of assisting you to reach a still clearer understanding of the distinction between thought and sensation, the bondage of the latter and the liberty of the former. Let us consider the contrast between the two. When a man feels a sensation (say the scratch of a pin), the sensation never disengages itself from itself in such a way as to make the man feel other sensations. The feeling of a sensation is never the feeling of that sensation and of other sensations besides; it is the feeling of that sensation only. Hence sensation, each sensation, is
