  Propositionalists were by no means rare in the 19th century, Gottlob Frege being the best known example. The Czech philosopher and mathematician Bernard Bolzano also deserves special mention. In his Wissenschaftslehre, or Theory of Science, published in 1837, he argued for the existence of what he called ‘Sätze an sich,’ or sentences in themselves, which he clearly distinguished from linguistic items or mental phenomena.  They are the fundamental bearers of truth and falsity, and the objects of the attitudes.  It is the goal of every science, including mathematics, to state the fundamental true sentences in themselves pertaining that subject matter. (This marks a clear departure from the psychologizing approaches of many of Bolzano’s contemporaries.)  Like Frege after him, Bolzano conceived of propositions as complexes composed of wholly abstract mind-independent constituents (Vorstellungen an sich). Bolzano’s work has had a profound influence on Husserlian phenomenology and the development of modern logic.