Given a proposition s and two sequences of ideas i_1...i_n and j_1...j_n, each idea i_k is replaced uniformly (wherever it occurs) by the corresponding j_k

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