Students and consumers of psychological science are routinely taught that the scientific approach used in psychological research facilitates its providing the most accurate information about human behavior. Because this approach to knowledge acquisition is supposed to be based on objective evidence and systematic reasoning rather than the biased interpretation of other approaches, these other approaches are often marginalized as being inferior. Critics of these claims assert that psychological science is subject to biases just as other approaches are and that the philosophy of naturalism not only pervades, but is also hidden and largely unquestioned in mainstream psychology. This study examines this claim, beginning with a dialectical contrast between naturalistic and non-naturalistic cultures to concretize practical features of naturalism and non-naturalism. It then uses those features to frame an in-depth analysis of introductory psychology textbooks where a compendium of the important settled principles and findings of all major sub-areas of the discipline should be found. Results show that naturalistic features are to be found throughout all the sub-areas of psychology and that non-naturalistic features are absent or marginalized in the texts.