• We say that a sentence is factually significant to any given person, if, and only if, he knows how to verify the proposition which it purports to express.

    A.J. Ayer: We say that a sentence is factually significant to any given person, if, and only if, he knows how to verify the proposition which it purports to express.
    'Language, Truth, and Logic' (2nd ed., 1946) p. 35