Accounts of category-based inductive reasoning can be distinguished by the emphasis they place on structured versus unstructured knowledge. In addition, it has been claimed that certain domains of structured knowledge are more available than others. Using a speeded task paradigm, participants rated the strength of inductive arguments in which the categories were either strongly or weakly associated and shared a taxonomic or causal relation.. Strongly associated categories received higher inductive strength ratings than weakly associated category pairs, regardless of the domain by which the categories were related. Strength of association was highly predictive of inductive strength ratings, but more additional variance was accounted for by beliefs about taxonomic and causal relations when people were not under time pressure. This suggests that, regardless of knowledge domain, maximizing inductive potency relies on the use of both structured and unstructured knowledge, depending on available mental resources.