 We shall say that a predicate \(\Tr(x)\) is a truth predicate for language \(\mathcal{L}\) only if \(\Tr(\left\ulcorner A\right\urcorner)\) is well-formed for every sentence \(A\) of \(\mathcal{L}\). We typically expect \(\Tr\) to obey some principles governing its behavior on sentences of a given language. It is to those we now  turn.[3]