Within the debate on the inevitability versus contingency of science for which Hacking’s writings have provided the basic terminology, the devising of counterfactual histories of science is widely assumed by champions of the contingency thesis to be an effective way to challenge the inevitability thesis. However, relatively little attention has been devoted to the problem of how to defend counterfactual history of science against the criticism that it is too speculative an endeavor to be worth bothering with—the same critique traditionally (...) levelled against the use of counterfactuals in general history. In this paper, we review the defense of counterfactuals put forward by their advocates within general history. According to such defense—which emphasizes the essential role of counterfactuals within explanations—good counterfactual scenarios need to exhibit the right kind of plausibility, characterized as continuity between said scenarios and what historians know about the world. As our discussion shows, the same requirement needs to be satisfied by good counterfactual histories of science. However, as we mention in the concluding part of the paper, there is at least one concern raised by counterfactual history of science as used to support the contingency thesis for which the defense based on the plausibility of the counterfactual scenarios does not seem to offer easy solutions. (shrink)