Gerd Buchdahl's main point has become somewhat dearer to me after long discussions with its author, with Ernest Gellner, and with J. W. N. Watkins. I have ultimately assumed that Buchdahl's thesis is that epistemological discussion is entirely useless for scientific research, a thesis very much in tune with the philosophy now in vogue. I shall try to criticise this thesis of Buchdahl's, and to argue that in the historical case which he chose to discuss as an illustration of his point — Dumas's views of atomism — epistemological criticism might have been of great use as a tool for solving scientific problems. The point of view from which my criticism is launched is that of Popper, as I shall explain in the body of my discussion.