Foundationalism concerns philosophical theories of knowledge resting upon justified belief, or some secure foundation of certainty such as a conclusion inferred from a basis of sound premises. Its main rival is coherentism, whereby a body of knowledge, not requiring a secure foundation, can be established by the interlocking strength of its components, like a puzzle solved without prior certainty that each small region was solved correctly. Identifying the other options to be either circular reasoning or infinite regress, thus the regress problem, Aristotle found the clear choice to be foundationalism, which posits basic beliefs underpinning others. Descartes, the most famed foundationalist, discovered a foundation in the fact of his own existence and the "clear and distinct" ideas of reason, whereas Locke saw foundation in experience. A foundation reflects differing epistemological emphases—empiricists emphasizing experience, rationalists emphasizing reason—but may blend both. In the 1930s, debate over foundationalism revived. Whereas Schlick viewed scientific...