Full Idea
A statement is directly verifiable if it is either itself an observation-statement,or is such that in conjunction with one or more observation-statements it entails at least one observation-statement which is not deducible from these other premises alone.
Gist of Idea
Directly verifiable statements must entail at least one new observation statement
Source
A.J. Ayer (Introduction to 'Language Truth and Logic' [1946], p.17)
Book Reference
Ayer,A.J.: 'Language, Truth and Logic' [Penguin 1974], p.17
A Reaction
This is the 1946 revised version of the Verification Principle, which was then torpedoed by an elaborate counterexample from Alonzo Church. Ayer thereafter abandoned attempts to find a precise statement of it.