In the history of philosophy, various definitions and criteria of truth have been proposed with the intention of grasping a particular aspect of it that would then allow it to be recognised in propositions or judgements. In this chapter, we focus on three paradigmatic conceptions that define truth as correspondence, as intersubjective coherence and agreement and, finally, as practical utility. After emphasising the problematic aspects of each definition, we shall show the common thread represented by the adequation (adaequatio) to which the truth of a proposition or assertion is always subordinate. Our main aim is to bring out a common trait of the various theories of truth, namely that the very attempt to define it ends up by relativising it, thus detracting from its absoluteness, which, on the contrary, as we shall show in the following chapters, constitutes the authentic essence of truth itself. Adequation, in fact, is always to something else, be it the (supposedly) external reality, a system (other than the proposition) or that which is useful to life (thus other than the belief held to be true). This means that these conceptions do not intend to grasp the truth in its absoluteness, but only the relative truth of a proposition, without, however, making it clear that relative truth is involved, thus replacing absolute truth with relative truth.