 So too, Bolzano clearly thinks, with propositions in themselves. Given a proposition, we can think of others just like it except for having different parts (ideas) at certain places. And though there can be no actual variation, i.e., no change in time, in the realm of propositions in themselves, nor any places strictly speaking, we can nonetheless speak metaphorically of making substitutions at certain places within propositions, using this as a façon de parler about atemporal relations between propositions and their parts. Given a proposition, then, we can consider certain of its parts variable, i.e., subject to replacement by other parts, and, given classes of suitable substituends for each site of substitution, we can again determine a class of propositions.