The age-old question “What is truth?” is not an unambiguous one. There are at least two different meanings. In one sense, it is a semantic question about the meaning of the word “truth” and/or a metaphysical question about the nature of the property of truth, that is, how truth can be defined in terms of other notions, if it is definable at all. In another sense, it is an epistemological question about the criterion or test of truth, that is, how we can recognize or accept (empirical) propositions as true. Ayer, in Language, Truth and Logic (LTL) and some other articles, tried to convince us that when we attempt to elucidate a theory of truth, we are only engaging in the epistemological project of finding the criterion of truth. This anti-semantical and anti-metaphysical view is based on Ayer’s (radical) deflationism about truth. In this chapter, I will argue that since Ayer did not accept that the criterion of truth is intimately related to the concept of truth, he can be seen as a deflationist about the nature of truth and as an advocate of a certain (Schlickian) kind of correspondence conception about the criterion of truth. His position would not be tenable if he had maintained what some of his contemporaries accepted, namely that there is a close connection between the two truth-theoretical tasks: the definitional and the criterial one.