This paper has a twofold purpose. First, it aims at highlighting one difference in how counterfactuals work in general history, on the one hand, and in history of the natural sciences, on the other hand. As we show, both in general history and in history of science good counterfactual narratives need to be plausible, where plausibility is construed as appropriate continuity of both the antecedent and the consequent of the counterfactual with what we know about the world. However, in general (...) history it is often possible to imagine a consequent dramatically different from the actual historical development, and yet plausible; in history of science, due to plausibility concerns, imagining a consequent far removed from the results of actual science seems more complicated. The second aim of the paper is to assess whether and to what degree counterfactual histories of science can advance the cause of the so-called “contingency thesis,” namely, the claim that history of science might have followed a path leading to alternative, non-equivalent theories, as successful as the ones that we currently embrace. We distinguish various versions of the contingency thesis and argue that counterfactual histories of science support weak versions of the thesis. (shrink)