 The domain of natural philosophy was “the common course of nature” (Biard 2001: 79, 80): it dealt with what occurred (in Aristotle’s phrase) “either always or for the most part” (ē tou aei ē tou hōs epi to polu) (Met. 1027a21–22). But there existed phenomena that fell outside this domain, namely miracles and marvels. Miracles, in the strict sense, were supernatural occurrences, which fell in the domain of theology. But marvellous phenomena were often thought of as “preternatural,” that is to say, as brought about by occult but natural properties and powers (Daston 1991: 95–100). Such powers included the influence exercised by the heavenly bodies on earthly affairs, as well as mysterious properties of sublunary entities, such as the lodestone. These powers were occult in the sense of being hidden. But they were also mysterious in that their workings were not explicable in terms of what Aristotelians believed to be the four simple substances (earth, air, fire, and water) and their associated primary qualities (the hot and the cold, the moist and the dry) (Pasnau 2011: 44). It is for this reason that they could not be proved to exist by demonstrative arguments, but could be known only by experience. This gave rise to a particular form of empiricism associated with the study of “natural magic.”