 In Tarski’s case, the stratification is obtained in the following way. Assume one wants to equip a language \(L_0\) with a truth predicate. From Tarski’s theorem (Section 2.1) it is known that this truth predicate cannot be part of the language \(L_0\) itself—at least not as long as we want the truth predicate to satisfy schema \(T\). Instead one builds a hierarchy of languages, \(L_0, L_1, L_2,\ldots\), where each language \(L_{i+1}\) has a truth predicate \(T_{i+1}\) that only applies to the sentences of \(L_j, j\le i\). In this hierarchy, \(L_0\) is called the object language and, for all \(i, L_{i+1}\) is called the meta-language of \(L_i\). This hierarchy effectively blocks the liar paradox, since now a sentence can only express the truth or untruth of sentences at lower levels, and thus a sentence such as the liar that expresses its own untruth cannot be formed.