  It is perhaps surprising to find a ‘five elements’ theory defended still in the seventeenth century. Some modern writers have tried to represent these substances as metaphors for different ‘states’ of matter—solid (earth), liquid (water), gas (air), and temperature (fire). This is, however, improbable, for it is nowhere said that a particular substance can turn from earth to water to air. Perhaps it is a mistake to see the theory as belonging to physics at all; instead, bearing in mind the way the substances are defined in terms of their sensible qualities, we might see it as an exercise in the logical analysis of the data presented by the various sense modalities to construct a (metaphysical) theory of the world. Such a theory would, for example, explain the fact that there are correlations between what we see and what we touch by positing that there must be types of things which can be both seen and touched. Likewise, the occurrence of tactile sensations with no correlated visual sensations leads us to postulate the existence of substances which can be felt but not seen (air), and so on for the other substances. It is, after all, the existence of such correlations between different sense modalities which grounds an objective conception of the world (phenomena accessible only by one sense are more likely to be thought of as subjective in origin).