I shall consider some points which bear on certain general methods of argument that Shoemaker uses in his book, Self-Knowledge and Self-Identity. They are methods of argument that enjoy considerable currency, and Shoemaker's very effective use of them invites one to consider their validity.

The first sentence of Shoemaker's book is: ‘What we mean when we assert something to be the case cannot be different from what we know when we know that thing to be the case’ (p. 1). This is incontestable, if it is taken to claim merely that no equivocation on ‘P’ is involved in ‘X asserts that P’ and ‘X knows that P’. In this form, while the principle is incontestable, it is also not of much philosophical use; in particular, not of much use for combating scepticism. Scepticism is compatible with it, and indeed can be partly based upon it; as when the sceptic claims that what we mean in making assertions about, say, other minds, refers to something sufficiently inaccessible for us not to be able to know anything about other minds.

The principle gets into a philosophical stride when assisted by certain other considerations. Thus there may be two classes of propositions A and B such that (a) B is the class of what would normally be called reports of tests, experiments, or observations relevant to the truth of the members of A, but (b) there is no way of coming to know members of A more direct than through knowing members of B.