We have spoken of soul as the cause of the plant life in our bodies, but plants were not admitted by the Stoics to be possessed of soul in the strict sense. What animated them was 'nature' or, as we have called it above, 'growth'. Nature, in this sense of the principle of growth, was defined by the Stoics as 'a constructive fire, proceeding in a regular way to production,' or 'a fiery spirit endowed with artistic skill'. That Nature was an artist needed no proof, since it was her handiwork that human art essayed to copy. But she was an artist who combined the useful with the pleasant, aiming at once at beauty and convenience. In the widest sense, Nature was another name for Providence, or the principle which held the universe together, but, as the term is now being employed, it stood for that degree of existence which is above cohesion and below soul. From this point of view, it was defined as "a cohesion subject to self originated change in accordance with seminal reasons effecting and maintaining its results in definite times, and reproducing in the offspring the characteristics of the parent". This sounds about as abstract as Herbert Spencer's definition of life, but it must be borne in mind that nature was all the time a 'spirit', and as such a body. It was a body of a less subtle essence than soul. Similarly, when the Stoics spoke of cohesion, they are not to be taken as referring to some abstract principle like attraction. 'Cohesions,' said Chrysippus, 'are nothing else than airs, for it is by these that bodies are held together, and of the individual qualities of things which are held together by cohesion, it is the air which is the compressing cause which in iron is called "hardness", in stone "thickness" and in solver "whiteness"'. Not only solidarity then, but also colours, which Zeno called 'the first schematisms' of matter were regarded as due to the mysterious agency of air. In fact, qualities in general were but blasts and tensions of the air, which gave form and figure to the inert matter underlying them. As the man is in one sense the soul, in another the body, and in a third the union of both, so it was with the cosmos. The word was used in three senses-- (1) God (2) the arrangement of the stars, etc. (3) the combination of both.