William of Ockam (c. 1280–c. 1349), known as the “More than Subtle Doctor,” was a Franciscan monk. He studied theology at Oxford and developed a strong expertise in logic, which may have led to his foundational empirical insights. Empiricism, as a doctrine independent of theology, was not widely accepted by medieval scholastic philosophers, so neither was the principle that came to be known as Ockam’s Razor: “Plurality is not to be assumed without necessity.” In its modern form in science, Ockam’s Razor is a rule for parsimony and simplicity in the construction of theories, and against commitment to more entities than are strictly necessary for the explanation of data or observations.

Ockam’s empiricism also applied to universals, and he rejected all claims to their reality. The only real things, according to Ockam, were existent particulars. He held that universals were the names of concepts, a doctrine called conceptualism. He asserted that there was no willed causation in nature, which entailed that even God could not interfere in physical causal laws. Although Ockam did believe that God could intervene in human cognition.