The coming-to-be of different physical substances in the world, as well as their various properties, is explained through the concept of mixture (krasis). Every physical thing in the world, in particular the biological world, is composed from mixtures of the fundamental elements; it is thus appropriately described in terms of the predominance of one or more qualities (hot, cold, etc.) within the mixture. Galen holds that higher-level properties come about through the alteration that may take place in this process of mixture; at the same time, the fundamental, low-level properties—hot, cold, wet and dry—which predominate in a given body remain powerful explanantia of its nature, at the macroscopic, perceptible level too; and this applies, for example, both to human bodies and to the various things they may eat and drink, including both food substances and drugs.