 Because for each objectual idea there are infinitely many other equivalent ones, we cannot determine relative probabilities simply by counting variants. It could be done, however, if the class of substitutions were restricted as in the case of relative validity by only allowing one idea among all those equivalent to a given one to be included in the class of substituends, provided that the resulting classes were finite (Bolzano sets out a different proposal in TS, §161, no. 7).