=183.= Quality (ποιότης, τὸ ποιόν, _qualitas_) constitutes the second category. It is defined by the Stoics as a difference in a substance which cannot be detached from that substance, but makes it ‘such and such,’ as for instance ‘sweet,’ ‘round,’ ‘red,’ ‘hot[57].’ Qualities, say the Stoics, are bodies[58]. This paradoxical statement may be understood in two ways; first, in that qualities do not exist independently, but are aspects of ‘body’ which possesses quality; secondly, in that qualities are bodies in a secondary sense. We may consider it evidence of the second point of view that language describes the qualities by nouns, as ‘sweetness,’ ‘rotundity,’ ‘redness,’ ‘heat’; and indeed it is not so long since our own chemists described heat as a ‘substance’ under the name of ‘caloric.’ This point of view is carried to an extreme when the Stoics say ‘qualities are substances,’ thus throwing the first two categories into one[59]. Much stronger is the tendency towards Aristotle’s views, so that as substance becomes identified with dead matter, quality is explained as the movement, tension, or current which endows it with life. Hence the Stoics say ‘the movement of rarefaction is the cause of quality[60]’; ‘matter is a dull substratum, qualities are spirits and air-like tensions[61]’; ‘quality is a spirit in a certain disposition[62]’; ‘the air-current which keeps each thing together is the cause of its quality[63].’ All these expressions must however be interpreted in the light of the Stoic theory as a whole. Finally we notice that, corresponding to the two kinds of substance, general and particular, there are two kinds of quality, as shewn in the ‘generically qualified’ (κοινῶς ποιόν) and the ‘individually qualified’ (ἰδίως ποιόν); for instance, heat in the universe and heat in particular objects[64]. [Sidenote: Disposition.] =184.= The third category is that of ‘disposition’ (πὼς ἔχοντα, _res quodammodo se habens_). It differs from quality in its variableness; for a brave man is always brave, and fire is always hot; but a man is sometimes standing, sometimes lying; fire is sometimes lambent, sometimes still. Qualities therefore appear to correspond generally to the συμβεβηκότα (_coniuncta_) of Epicurus, in that they can never be separated from a body[65]; and dispositions rather with the συμπτώματα (_eventa_), which come and go[66]. The third category appears to be used by the Stoics in a very wide sense, and to correspond to several of the categories of Aristotle[67]. Disposition is attached to quality as quality is attached to substance[68]; and though dispositions are not expressly termed bodies, yet we must consider them to be, as the terms in the Greek and Latin sufficiently indicate, bodies in particular aspects.