 Concerning Theophrastus’ account of the four elements, it has been debated to what extent this conforms to the Aristotelian doctrine. In particular, it is not clear whether Theophrastus followed Aristotle in holding that the heavens are made of a fifth element, the ether, distinct from the four sublunary elements, or whether he claimed that the heavens are simply made of fire (frs. 158–168 FHS&amp;G). It has been argued, for instance, that Theophrastus abandoned the fifth element, but used it only in arguments against Plato without endorsing it himself (see Steinmetz 1964). There is no doubt, on the other hand, that he gave prominence to the element of fire. In his short treatise On Fire, Theophrastus distinguished heavenly fire from terrestrial fire, which is always mixed with other elements, and pointed out that, in contrast to the other three elements, terrestrial fire can be generated artificially and constantly requires refuelling. Most importantly, Theophrastus postulated that fire, or heat, is active while the other three elements are passive (fr. 177 FHS&amp;G). In fact, this Theophrastean view has been interpreted as a serious departure from Aristotle’s physics, according to which hot and cold are active while moist and dry are passive. Against this interpretation, however, it has been remarked that, since the Aristotelian biology postulates only the hot as active, Theophrastus did nothing but extend Aristotle’s view to physics in general (see Longrigg 1975). Furthermore, although some scholars have presented the action of the hot as constituting for Theophrastus the reason for the interchanges between the elements, others have counterclaimed that these should be understood as qualitative and not just due to a mechanical mixture (see Steinmetz 1964; Gottschalk 1967).