A retrospective appreciation of Willard Day's contributions to radical behaviorism and the analysis of verbal behavior.

Willard Day's contributions to radical behaviorism are grouped under three headings: (a) an emphasis on the distinction between radical and methodological behaviorism; (b) an emphasis on the interpretation, rather than the prediction and control, of behavior; and (c) an emphasis on the analysis of verbal behavior as a natural, ongoing phenomenon. The paper suggests that the contributions above are listed in ascending order of significance.