Goldman's accounts of knowledge and justified belief, using notions like causation and reliability instead of normative concepts like permissibility and obligation, contributed to a philosophical approach that came to be known in the 1970s as naturalized epistemology. (Unlike W.V.O. Quine's version of naturalized epistemology, however, Goldman's retains a traditional focus on questions of justification.) Goldman's view emerged initially as part of the efforts in the 1960s to find a "fourth" condition in response to the Gettier challenge to the account of knowledge as "justified true belief." In his 1967 paper, "A Causal Theory of Knowing", Goldman proposed that knowledge amounts to true belief appropriately caused by the fact that makes it true. Later, he claimed knowledge amounts to true belief that is produced by a reliable process.