In the further applications of Stoic theory disposition as defined above appears to be replaced in Greek by the term ἕξις. But this term is used in two different senses. In the first place it is the movement of rarefaction and condensation, by which a spirit or thrill passes from the centre of an object to the extremities, and returns from the extremities to the centre[69]; in this sense it is translated in Latin by _unitas_, and takes bodily form as an air-current[70]. This force, when it requires a further motive power in the direction of development, becomes the principle of growth (φύσις, _natura_), and is displayed not only in the vegetable world, but also in animals, as in particular in the hair and nails[71]. Growth when it takes to itself the further powers of sensation and impulse becomes soul (ψυχή, _anima_), and is the distinctive mark of the animal world[72]. In a rather different sense ἕξις or temporary condition is contrasted with διάθεσις or ‘permanent disposition.’ In this sense the virtues are permanent dispositions of the soul, because virtue is unchanging; the arts are temporary conditions. The virtues belong to the wise man only, the arts to the ordinary man. This distinction however does not hold its ground in the Roman period, the word _habitus_ (representing ἕξις), our ‘habit,’ being used in both senses[73]. The virtues are bodies, being dispositions of the soul which is bodily[74]. [Sidenote: Relative position.] =185.= The fourth category, that of ‘relative position’ (πρός τί πως ἔχον) appears to be of less importance than the others[75]. Its characteristic is that it may disappear without altering that to which it belongs. Thus that which is on the right hand may cease to be so by the disappearance of that which was on its left; a father may cease to be such on the death of his son[76]. It seems difficult to describe the fourth category as one consisting of ‘body,’ but at least it is a function of body. Also it does not appear that ‘relative position’ can be predicated of the universe as a whole; it is peculiar to individual objects, but works towards their combination in a larger whole. The fourth category has an important application in practical ethics in the doctrine of daily duties, for these are largely determined by the relative positions (σχέσεις) of the parties concerned: such are the duties of a king to his people, a father to his son, a slave to his master[77]. [Sidenote: Combination.]