Full Idea
In the improved version, a statement was verifiable, and consequently meaningful, if 'some observation-statement can be deduced from it in conjunction with certain other premises, without being deducible from those other premises alone'.
Gist of Idea
A statement is meaningful if observation statements can be deduced from it
Source
A.J. Ayer (Introduction to 'Language Truth and Logic' [1946], p.15)
Book Reference
Ayer,A.J.: 'Language, Truth and Logic' [Penguin 1974], p.15
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. Hence a 1946 revised version had to be produced.