 Some sciences, e.g., number theory or real analysis, consist entirely of purely conceptual propositions, and are accordingly called purely conceptual sciences. Though Bolzano optimistically held that most purely conceptual truths could be known a priori, he refrains from claiming this of all of them, and clearly recognizes that many purely conceptual propositions, even in mathematics, are accepted based at least partly on empirical (intuitional) evidence (TS, §133; Bolzano 2004a: 53). 