In 1987, Altman and Rogoff shared their insightful analysis of the various and often conflicting worldviews underlying the work of research psychologists, particularly those whose focus was on understanding the relationships between people and the environment. Their taxonomy classified the range of peopleenvironment relational research into four perspectives: trait, interactional, organismic, and transactional. In the decades since, environmental design research has continued to morph, into a field in which there is no doubt a multiplicity of viewpoints at work. This paper explores the epistemological assumptions found in major approaches to inquiry within environmental design research. It does so in relation to the condition of environmental design practice as being largely intuitive and tacit. A focus is upon the nature of evidence within each paradigm leading to a timely consideration of the concept of “evidence-based design” (Hamilton, 2006). Since the nature of knowledge varies between paradigms, and evidence is that knowledge which compels acceptance by the mind of a truth, how one would define evidence-based design may very well depend upon one’s mode of thinking. Herein lays the danger of current discussions within evidence-based design which has unspoken but powerful underlying assumptions regarding the nature of evidence and the nature of the problem. These assumptions are explicated and addressed within the diversity of research approaches undertaken within design inquiry. Discussion will highlight the need for a more inclusive definition of evidence within environmental design given the nature of the architectural enterprise as necessarily projective. From this perspective, valued evidence is more strongly related to prediction (forecasting) than explanation; hence the continuing reliance on tacit knowledge in the design process (Schon, 1983). If evidence-based design is to concern itself with developing knowledge that may inform the design process, a richer understanding of the epistemological underpinnings is necessary to further the dialogue on the nature of applicable research.