This is the first complete English translation of Bernard Bolzano's four-volume Wissenschaftslehre or Theory of Science, a masterwork of theoretical philosophy. Bolzano (1781-1848), one of the greatest philosophers of the nineteenth century, was a man of many parts. Best known in his own time as a teacher and public intellectual, he was also a mathematician and logician of rare ability, the peer of other pioneers of modern mathematical logic such as Boole, Frege, and Peirce. As Professor of Religion at the Charles University in Prague from 1805, he proved to be a courageous and determined...