 it must be possible to eliminate \(F\) from any argument involving it. But, if we try to replace \(F\) by its definiens, we obtain \(F(F) \equiv \neg F(F)\), and we are trapped in an infinite regress, as there is no \(F\)-free expression that could replace \(F(F)\). So the contradiction is ascribed to an error in the theory of definitions, namely to the use of definitions that give rise to an infinite chain of substitutions, without converging to a result. Behmann’s technical proposal consists in a reformed logic without types but with an added operator ! which, when given a predicate \(\chi\), singles out exactly those arguments \(x\) to which \(\chi\) meaningfully applies. For instance, the syllogism Barbara, usually stated in the form