 Theories of signification were complicated by the metaphysical problem of common natures. If we say that words signify not only concepts but things external to and independent of the mind do we mean that ‘human being’ and ‘tall’ signify special common objects such as humanity or tallness, or do we mean that they signify Socrates and his quality of being tall? For Aquinas, who did not want to give common natures any kind of intermediary existence independent of both concepts and actual things, the significate (significatum) of a term was the intellect’s conception (whether simple or definitional) of the thing signified; the thing signified (res significata) was usually the property or the nature characterizing individual external objects; and the referent (suppositum) was the individual external object itself, viewed as the bearer of the property or nature. However,‘human being’ cannot be said to  signify  Socrates, since the mind cannot conceive physical individuals as such. In the fourteenth century, further developments took place. There was a new focus on the notion of a mental language superior to spoken language, and concepts, as parts of this mental language, were themselves regarded as having signification. Moreover, Scotists and nominalists agreed that, at least in principle, physical individuals could be conceived as such. William of Ockham and his followers not only denied the existence of common natures but insisted that spoken words did not signify concepts. As a result, both spoken words and the concepts to which spoken words are subordinated have the same significates, namely individual things and their individual properties, such as the tallness of Socrates. Other nominalists, notably Buridan, insisted that spoken words did signify concepts as well as individuals, for concepts are required to mediate between spoken words and individual things.