There appears to be a confusion here of two quite different things: the Cartesian position and the identification of knowing as a fact in the inner life of a subject with knowledge as the representation of a content known. The essence of the Cartesian position, as everybody knows, is that some of the things of which we are conscious we know so absolutely as to make doubt an absurdity and an impossibility. Whether Descartes did or did not maintain more than that; whether he did or did not hold that all of the facts of which we are conscious we know in the same absolutely certain way, is not a matter of consequence save from the point of view of history. The important point is, that he need not have maintained it. Because he knew some of the facts of which he was conscious so certainly as to make doubt an impossibility, he was not required to say that all of the facts of which he was conscious could be put in the same category unless as the result of an introspective examination. But introspection compelled him to take no such position. Introspection shows that some of the states of consciousness we know in an absolutely certain way and that some others are in a state of utter uncertainty. To require me to hold that, if I claim to know some of my inner states with absolute certainty, I must make the same claim of all, is as absurd as it would be to require a man to hold that he can see an atom of hydrogen because he claims to be able to see a drop of water. And to hold that, because I may be mistaken as to what is in my consciousness when I use general names intelligently, I may be mistaken in supposing that when I am in severe pain I know that I am, is like saying that, because I cannot see an atom of hydrogen, therefore I cannot see a drop of water. In no fruitful sense, therefore, can we say that we assume that what we feel we do feel, when we are trying to draw distinctions between assumption and knowledge.
But when Bain says that the uniformity of nature is another assumption, I agree with him fully. "Water has quenched our thirst in the past. By what right do we affirm that the same will happen in the future? Experience does not teach us
