This paper is a critical analysis of a debate between behavioristic and phenomenological/existentialist approaches to the human subject, which unfolded in the Porstmouth Symposium of 1967 on Design Methods in Architecture. Part of the so-called design methods movement, a cycle of events and publications that aimed at a cross-disciplinary elucidation of design, the Portsmouth Symposium epitomized a critique to the rationalist approaches of the movement's early years and a turn toward subjectivity and the human sensorium. In this paper I argue that phenomenological and existentialist arguments did not dethrone the design methods movement’s positivist attitude to design, but were incorporated in the movement’s aspiration to systematize design and anticipate its social outcomes. Using the Portsmouth Symposium’s published proceedings as source material, the paper is structured in terms of position and opposition. I begin by presenting the rationalist/behaviorist approach to human-environment associations, grounded on Christopher Alexander and Barry Poyner’s earlier research on human tendencies. Consecitively, I outline the phenomenological/existentialist objections to the behaviorist stance, cast from the perspective of philosophy (Janet Daley), ethics (Janet Daley, Amos Rapoport, Tony Ward), and psychology (Jane Abercrombie). I close the paper by discussing the conference organizers’ efforts to integrate the three objections in the design methods agendas. By orchestrating a synergy among psychology, philosophy and scientific rigor, the Portsmouth Symposium framed a critique of reason and found a reasonable way to address it. In doing so, it bridged the design methods movement’s positivist impulses with its participants’ humanistic aspirations.