Naturalized epistemology is a collection of philosophic views about the theory of knowledge that emphasize the role of natural scientific methods. This shared emphasis on scientific methods of studying knowledge shifts the focus of epistemology away from many traditional philosophical questions, and towards the empirical processes of knowledge acquisition. There are noteworthy distinctions within naturalized epistemology. Replacement naturalism maintains that we should abandon traditional epistemology and replace it with the methodologies of the natural sciences. The general thesis of cooperative naturalism is that traditional epistemology can benefit in its inquiry by using the knowledge we have gained from cognitive sciences. Substantive naturalism focuses on an asserted equality of facts of knowledge and natural facts.
The name for such epistemology was coined in the 20th century by W. V. O. Quine. Objections to naturalized epistemology have targeted features of the general project as well as characteristics of specific versions. Some objectors argue that natural scientific knowledge cannot be circularly grounded by the knowledge obtained through cognitive science, which is itself a natural science. This objection from circularity has been aimed specifically at strict replacement naturalism. There are similar challenges to substance naturalism that maintain that the substance naturalists' thesis that all facts of knowledge are natural facts is not only circular but fails to accommodate certain facts. Several other objectors have found fault in the inability of naturalized methods to adequately address questions about what value forms of potential knowledge have or lack.
Forms of naturalism
Replacement naturalism
W. V. O. Quine's version of naturalized epistemology considers reasons for serious doubt about the fruitfulness of traditional philosophic study of scientific knowledge. These concerns are raised in light of the long attested incapacity of philosophers to find a satisfactory answer to the problems of radical scepticism and, more particularly, to David Hume's criticism of induction. But also, because of the contemporaneous attempts and failures to reduce mathematics to pure logic by those in or philosophically sympathetic to The Vienna Circle. Quine concludes that studies of scientific knowledge concerned with meaning or truth fail to achieve the Cartesian goal of certainty. The failures in the reduction of mathematics to pure logic imply that scientific knowledge can at best be defined with the aid of less certain set-theoretic notions. Even if set theory's lacking the certainty of pure logic is deemed acceptable, the usefulness of constructing an encoding of scientific knowledge as logic and set theory is undermined by the inability to construct a useful translation from logic and set-theory back to scientific knowledge. If no translation between scientific knowledge and the logical structures can be constructed that works both ways, then the properties of the purely logical and set-theoretic constructions do not usefully inform understanding of scientific knowledge.
Cooperative naturalism
Cooperative naturalism is a version of naturalized epistemology which states that while there are evaluative questions to pursue, the empirical results from psychology concerning how individuals actually think and reason are essential and useful for making progress in these evaluative questions. This form of naturalism says that our psychological and biological limitations and abilities are relevant to the study of human knowledge. Empirical work is relevant to epistemology but only if epistemology is itself as broad as the study of human knowledge.
Substantive naturalism
Substantive naturalism is a form of naturalized epistemology that emphasizes how all epistemic facts are natural facts. Natural facts can be based on two main ideas. The first is that all natural facts include all facts that science would verify. The second is to provide a list of examples that consists of natural items. This will help in deducing what else can be included. However, Quine points out that these concerns with validation are merely a byproduct of traditional epistemology. But without the normative, there is no "justification, rational acceptability [nor] warranted assertibility". Ultimately, there is no "true" since any method for arriving at the truth was abandoned with the normative. Notions which explain truth are intelligible only when the normative is presupposed. Moreover, for there to be "thinkers", there "must be some kind of truth"; otherwise, "our thoughts aren't really about anything [,...] there is no sense in which any thought is right or wrong".
Jaegwon Kim, another critic of naturalized epistemology, further articulates the difficulty of removing the normative component. He notes that modern epistemology has been dominated by the concepts of justification and reliability. Kim argues that epistemology and knowledge are nearly eliminated in their common sense meanings without normative concepts such as these. These concepts are meant to engender the question "What conditions must a belief meet if we are justified in accepting it as true?". That is to say, what are the necessary criteria by which a particular belief can be declared as "true" (or, should it fail to meet these criteria, can we rightly infer its falsity)? This notion of truth rests solely on the conception and application of the criteria which are set forth in traditional and modern theories of epistemology.
Kim further explains how the notion of "justification" (alongside "belief" and "truth") is the defining characteristic of an epistemological study. To remove this aspect is to alter the very meaning and goal of epistemology, whereby we are no longer discussing the study and acquisition of knowledge. As Kim puts it, "If justification drops out of epistemology, knowledge itself drops out of epistemology." Justification is what makes knowledge valuable and normative; without it what can rightly be called true or false? We are left with only descriptions of the processes by which we arrive at a belief. Quine is moving epistemology into the realm of psychology, where Quine's main interest is based on the sensory input–output relationship of an individual. On Kim's view, this account cannot establish an affirmable statement that leads us to truth, since all statements without the normative are purely descriptive and so cannot amount to knowledge. The vulgar allowance of any statements as scientifically valid, but not "true", makes Quine's theory difficult to accept on any epistemic theory that requires truth as the object of knowledge.
In response, Quine insists that critics are wrong to suggest that, given his naturalized epistemology, "the normative element, so characteristic of epistemology, goes by the board. Insofar as theoretical epistemology gets naturalized into a chapter of theoretical science, so normative epistemology gets naturalized into a chapter of engineering: the technology of anticipating sensory stimulation." Thus, "[t]he normative is naturalized, not dropped." There remains debate, however, about whether Quine's view can account for the normativity of epistemology.
As a result of these objections and others like them, most contemporary philosophers agree that replacement naturalized epistemology may be too strong of a view (even Quine held more moderate views in later writings).