AbstractWe introduce a tool for analysing models of$\text {CT}^-$, the compositional truth theory over Peano Arithmetic. We present a new proof of Lachlan’s theorem that the arithmetical part of models of$\text {CT}^-$are recursively saturated. We also use this tool to provide a new proof of theorem from [8] that all models of$\text {CT}^-$carry a partial inductive truth predicate. Finally, we construct a partial truth predicate defined for a set of formulae whose syntactic depth forms a nonstandard cut which cannot be extended to a full truth predicate satisfying$\text {CT}^-$.