Meaning requires either logical truth or testability against experience

Ayer's central proposal, the verification principle, states that a sentence carries genuine factual content only under two conditions: it is analytic, meaning its truth follows purely from the definitions of its terms and logical structure, or it is synthetic and empirically verifiable, meaning some possible observation could in principle bear on whether it's true. A sentence failing both tests isn't simply false or unproven — Ayer insists it fails to say anything at all, however grammatically correct it appears.

This criterion was designed to do enormous philosophical work with minimal apparatus: rather than arguing point by point against specific metaphysical claims, Ayer wanted a single test that could sort all possible statements into meaningful and meaningless categories in one stroke, sidestepping centuries of inconclusive debate by declaring much of it simply outside the bounds of sense.

The boldness of this move is also its most exposed flank, since critics quickly asked whether the principle itself could pass its own test.

Takeaway: before treating a claim as merely unproven, ask Ayer's harder question — is there any conceivable observation that could count for or against it at all?