The standard technical vocabulary used to define placebo therapies and experimental placebo controls in medicine and psychiatry is both confusing and obscure. To achieve conceptual clarity in the theory of placebogenic phenomena, this paper offers a rigorous articulation of the placebo notion, a lucid new terminology that obviates the defects intrinsic to the traditional locutions employed in the placebo literature, and a substantial revamping of A. K. Shapiro's influential prior definition of 'placebo'. This paper supersedes an earlier version (Grünbaum, 1981).