Karl Raimund Popper was one of the twentieth-century’s most influential philosophers of science. Qualified to teach elementary school and to teach physics and mathematics at the secondary level, Popper received his Ph.D. in Philosophy from the University of Vienna in 1928. Popper’s first and most influential work was The Logic of Scientific Discovery (Logic der Forschung), originally published in 1934 and translated into English by Popper in 1959. Popper was critical of positivism and of the inductive mode of science, in which observation of singular instances could lead to universal claims. Even large numbers of singular instances, he claimed, could never conclusively demonstrate a universal claim.