The basic insight underlying Bolzano’s method of idea-variation is quite simple (WL II, 77 ff.). Let us take as our first example \(S_1\) the proposition [Kant is a German philosopher]. (In order to simplify matters linguistically, we do not adhere to Bolzano’s formulation ‘\(A\) has \(b\)’ but will allow also formulations of the kind ‘\(A\) is (a) \(B\)’. Moreover, we will take in what follows words like ‘German’, ‘French’, ‘European’, ‘American’ etc. in the sense of ‘born in Germany’, ‘born in