Full Idea
If there is no experience at all of finding out that one is not conscious, or that one does not exist, ..it is tempting to say that sentences like 'I exist', 'I am conscious', 'I know that I exist' do not express genuine propositions.
Gist of Idea
'I know I exist' has no counterevidence, so it may be meaningless
Source
A.J. Ayer (The Problem of Knowledge [1956], 2.iii)
Book Reference
Ayer,A.J.: 'The Problem of Knowledge' [Penguin 1966], p.48
A Reaction
This is, of course, an application of the somewhat discredited verification principle, but the fact that strictly speaking the principle has been sort of refuted does not mean that we should not take it seriously, and be influenced by it.