Let’s clarify the sense of condition (F) with an example. Consider a language LAr+ which is like LAr but has besides another individual constant, “2”, and another dyadic predicate, “Pd”, whose desired interpretations are the number 2 and the relation of being the immediate predecessor of, respectively. Let K be the following set of sentences of LAr+: {“∀x(Nx→¬Mx0)”, “N0”} (these sentences are true); and let X be the sentence “¬M00”. The argument with premises K and conclusion X is intuitively lo