Full Idea
The mark of a genuinely factual proposition is that some experiential propositions can be deduced from it in conjunction with certain other premises without being deducible from those premises alone.
Gist of Idea
Factual propositions imply (in conjunction with a few other premises) possible experiences
Source
A.J. Ayer (Language,Truth and Logic [1936], Ch.1)
Book Reference
Ayer,A.J.: 'Language, Truth and Logic' [Penguin 1974], p.52
A Reaction
I.Berlin showed that any statement S could pass this test, because if you assert 'S' and 'If S then O', these two statements entail O, which could be some random observation. Verificationism kept meeting problems of this kind.