 Many of the concepts analysed by philosophers have their origin in ordinary—or at least extra-philosophical—language. Perception, knowledge, causation, and mind would be examples of this. But the concept of substance is essentially a philosophical term of art. Its uses in ordinary language tend to derive, often in a rather distorted way, from the philosophical senses. (Such expressions as ‘a person of substance’ or ‘a substantial reason’ would be cases of this. ‘Illegal substances’ is nearer to one of the philosophical uses, but not the main one.) There is an ordinary concept in play when philosophers discuss ‘substance’, and this, as we shall see, is the concept of object, or thing when this is contrasted with properties or events. But such ‘individual substances’ are never termed ‘substances’ outside philosophy.