This was Egon Brunswik's first major statement of his vision of psychology (Hammond, 1966, p.534). That vision developed and matured over the 20 years following this early statement, but the continuity of the direction set here is clear and strong. This chapter focuses on Brunswik's vision as it takes shape in what came to be called his "probabilistic functionalism." In particular, we trace two important roots of his work: "Vienna Circle" positivism and European functionalism in the tradition of Franz Brentano. The story of this "mixed marriage" displays several interesting turns before it is told. Yet our interest in Brunswik is not primarily antiquarian. The place of positivism in Brunswik's approach is important for understanding the recently emerging subdiscipline of environmental psychology (cf. Stokols, 1977). Environmental psychology is part of a broad interdisciplinary area called variously "environment-behavior relations," 'social ecology," "environment-behavior research," "environmental design," and so forth.¹ While the mutual interdependence of environments, behavior, and experience has been a long-standing interest of psychologist in many subdisciplines, these concerns are receiving special attention from environmnental and community psychologists.