To date there seems to be no disciplined way of distinguishing between ad hoc hypotheses and legitimate auxiliary hypotheses. This is embarrassing not just for Popperian falsificationist scientific methodology, for the need for such a distinction seems an important part of scientific practice. Do scientists bother about ad hoc hypotheses at all? Did any towering figure in the history of science care about ad hoc hypotheses? Ironically, the answers to these questions seem to be “Yes” and “No” in both cases. (...) Inspired by Paglieri and Woods’ recent proposal for a theory of enthymeme based on the principle of parsimony, I propose to approach the problem of ad hoc hypothesis by interpreting it as a kind of enthymeme resolution. One reason for this interpretative strategy lies in its potential for understanding the pervasiveness and the longevity of the Aristotelian scientific methodology embedded in the scientific practice throughout the ages. (shrink)