By embracing naturalism as a philosophical method of investigation, Quine proposes a change in traditional epistemology: philosophy must be continuous with natural science, and, therefore, not based on a first philosophy dependent on a priori investigations. For Quine, metaphysics does not guarantee anything, and due to its method of verifiable hypotheses, science is the only and the best instrument of knowledge. In naturalism there is no difference of nature between science and philosophy because both relate experience and theory through language. In this dissertation, I argue that there are some weaknesses in this perspective on philosophical methodology and knowledge. My strategy is to analyze Quine s rejection of the notions of a priori and analytic and his claim that theories and their abstract aspects can be kept at the level of experience by combining naturalism with a behaviorist conception of language. I argue that the thesis of the underdetermination of theories by experience poses a problem for Quine s empiricism, and undermines a strong naturalism according to which theories depend exclusively on experience.