Of far more importance in the Stoic system than the study of logic was the study of nature. This branch of learning, notwithstanding an appeal to older views, was treated by them with more independence than any other. The subjects which it included may be divided under four heads, viz.: 1. Fundamental positions; 2. The course, character, and government of the universe; 3. Irrational nature; and 4. Man. [253] The present chapter will be devoted to considering the first of these groups—the fundamental positions held by the Stoics in regard to nature; among which three specially deserve notice—their Materialism; their Dynamical view of the world; and their Pantheism. [A. Materialism.] [(1) Meaning of the Stoic materialism.] [(a) Material or corporeal objects.] [(α) Reality belongs to material objects only.] Nothing appears more striking to a reader fresh from the study of Plato or Aristotle than the startling contrast to those writers presented by the Materialism of the Stoics. Whilst so far following Plato as to define a real thing [254] to be anything possessing the capacity of acting or being acted upon, the Stoics nevertheless restricted the possession of this power to material objects. Hence followed their conclusion that nothing real exists except what is material; or, if they could not deny existence in some sense or other to what is incorporeal, they were fain to assert that essential and real Being only belongs to what is material, whereas of what is incorporeal only a certain modified kind of Being can be predicated. [255] Following out this view, it was natural that they should regard many things as corporeal which are not generally considered such; for instance, the soul and virtue. Nevertheless, it would not be correct to say [256] that the Stoics gave to the conception of matter or corporeity a more extended meaning than it usually bears. For they define a body to be that which has three dimensions, [257] and they also lay themselves out to prove how things generally considered to be incorporeal may be material in the strictest sense of the term. Thus besides upholding the corporeal character of all substances, including the human soul and God, [258] they likewise assert that properties or forms are material: all attributes by means of which one object is distinguished from another are produced by the existence [(β) Theory of air-currents.] of certain air-currents, [259] which, emanating from the centre of an object, diffuse themselves to its extremities, and having reached the surface, return again to the centre to constitute the inward unity. [260] Nor was the theory of air-currents confined to bodily attributes. It was applied quite as much to mental attributes. Virtues and vices are said to be material, [261] and are deduced from the tension imparted to the soul by atmospheric substances therein subsisting. [262] For the same reason the Good is called a body, for according to