This, then, is Galen’s account of how a new type of substance comes about through the combination of two other substances. And here he makes the distinction between the kind of change where a substance affects another in just one or other of its qualities—heating it, for example, or heating it and drying it—and another, observed particularly in the assimilation of food, which involves change in respect of the whole substance (kath’ holēn tēn ousian, and similar expressions); the distinction is elaborated in Temp. (III.1, 270; III.4, 277; cf. Hipp. Elem. 9, 132–9), as well as in Galen’s theoretical work on the action of drugs, SMT, III.4); at Prop. Plac. (9, 84–7), he talks of the “specificity” or “specific quality” (idiotēs) of the substance considered as a whole. This specific quality, apparently, inheres in the substance, as something separate from its components. Galen here comes close to articulating a notion of emergent properties: he uses these notions of holē ousia and idiotēs not only in the context of drug properties, but also occasionally in that of the higher-level physiological capacities of the body, or even the soul, in accounts of the way in which an entity or its active capacities are qualititatively different from the underyling elements that went into its composition (Singer 2020a).