 This contrast is certainly found in some of the works attributed to Hippocrates (ca. 460–370 BCE). The author of one Hippocratic treatise argues against those who practice medicine on the basis of some general principle or postulate (hupothesis). Medicine, he suggests, does not require a general theory “about human nature [ho ti estin anthrōpos],” of the kind offered by Empedocles and other philosophers (AM 20.1). Such general principles may be required when dealing with with matters that are “obscure and dubious,” such as “the things in the sky or under the earth” (AM 1.3). But medicine differs from such speculative sciences, since its conclusions can be confirmed by experience. Of particular note here is the phrase “the things in the sky or under the earth,” which picks out the main areas of early Ionian science (Barnes 1982: 139; cf. Plato Ap. 18b8–9).