Many scholars point to the close association between early modern science and the rise of rational arguments in favour of the existence of witches. For some commentators, it is a poor reflection on science that its methods so easily lent themselves to the unjust persecution of innocent men and women. In this paper, I examine a debate about witches between a woman philosopher, Margaret Cavendish , and a fellow of the Royal Society, Joseph Glanvill . I argue that Cavendish is (...) the voice of reason in this exchange—not because she supports the modern-day view that witches do not exist, but because she shows that Glanvill’s arguments about witches betray his own scientific principles. Cavendish’s responses to Glanvill suggest that, when applied consistently, the principles of early modern science could in fact promote a healthy scepticism toward the existence of witches. (shrink)