Behaviorism as a school of psychology was founded by John B. Watson, and grew into the neobehaviorisms of the 1920s, 30s and 40s. Philosophers were involved from the start, prefiguring the movement and endeavoring to define or redefine its tenets. Behaviorism expressed the naturalistic bent in American thought, which opposed the then prevailing philosophical idealism and was inspired by developments in natural science itself, especially biology. This naturalism was not materialistic; it viewed mind as a part of nature from a Darwinian and functionalist perspective. Although Watson adopted a strict materialism, other behaviorists, including Tolman, Hull, and Skinner, were biologically oriented and rejected materialism and physicalist reduction. After the 1940s the character of philosophical naturalism in America changed. The physicalism of some logical empiricists and Quine became prominent, and behaviorism was philosophically reinterpreted in physicalist terms.