Full Idea
If I know that an object behaves in every way as a conscious being must, by definition, behave, then I know that it is really conscious. This is an analytical proposition.
Gist of Idea
A conscious object is by definition one that behaves in a certain way, so behaviour proves consciousness
Source
A.J. Ayer (Language,Truth and Logic [1936], Ch.7)
Book Reference
Ayer,A.J.: 'Language, Truth and Logic' [Penguin 1974], p.172
A Reaction
This treats the Turing test as proof of consciousness, and is open to all the usual objections to behaviourism. To say behaviour IS consciousness is ridiculous. It just counts as evidence. Presumably Ayer would later have become a functionalist.