Abstract

In this paper, I examine the transition from zymotic views of disease to germ views in Britain in the mid-1800s. I argue that neither realist nor anti-realist accounts of theory-change can account for this case, because both rely on a well-defined notion of theory, which, as the paper will show, is inapplicable in this instance. After outlining the zymotic theory of disease, I show that, even though it hardly had anything in common with the germ theory, it was highly successful. However, despite this success, it is not possible to identify stable elements that were carried over to the germ theory; thus, realists cannot account for the shift from one to the other. Anti-realists, however, don’t do much better: their focus tends to be on (radical) discontinuities across theories, yet the zymotic case does not exemplify this, either. Instead, there is a slow and complex evolution from zymotic to germ views, during which various zymotic elements are assimilated into the germ theory, until, eventually, none of the zymotic theory’s original elements are left.