The verifiability theory of meaning
In the early twentieth century, the logical positivists put forth what came to be known as the verifiability theory of meaning. The verifiability theory was based upon the verifiability principle, which states "A statement is literally meaningful (it expresses a proposition) if and only if it is either analytic or empirically verifiable." However, the verifiability principle is not empirically verifiable, though there is speculation that there is an analytic proof possible. Considerable misunderstanding exists as to the thought that the principle invalidates itself since some formulations of the theory do not mention analytic verifiability.
Prior to the development of the verifiability principle, Immanuel Kant classified statements into two categories, a set of analytic statements, and a set of synthetic statements . For Kant, the truth of a mathematical statement had to be determined inside the mind, and he called any such statement analytic, in contrast to a synthetic statement like "the sky is blue", which requires the use of sensory perception to verify.
The classification terms analytic/synthetic have fallen into disuse in contemporary formal logic, but the idea of a statement being empirically verifiable was taken up by in the twentieth century by the logical positivists of the Vienna Circle, who used it to build upon the theory of language that Ludwig Wittgenstein had introduced in his Logisch-Philosophische Abhandlung. In essence, Kant's synthetic statements are what are now called empirical statements. If an empirical statement is true, it ought to be empirically verifiable, and if an empirical statement is false, it ought to be empirically falsifiable. But, the verifiability priniciple is indeed an example of one of Kant's analytic statements. The verifiability theory of meaning is also closely related to the correspondence theory of truth.
The verifiability theory is an important argument for non-cognitivism.