171. Under the general heading of Physics the ancients included a number of subjects which in modern times form independent branches of philosophy. Cleanthes subdivided the subject into Physics proper and Theology[1]. Here it will be convenient to make a larger number of subdivisions, so as to treat separately of (i) the Foundations of Physics, generally called (after Aristotle’s treatise) ‘Metaphysics’; (ii) Physics proper, that is, the account of the Universe and its history; (iii) the final problems involved in the history of the Universe, such as its government by Divine Providence, the Existence of Evil, Free-will, and Chance; (iv) the problems of Religion, such as the existence of gods, their number, character, and claims on mankind; and (v) the nature of Man, including the modern subjects of Psychology and Physiology, and to some extent of Anthropology also, treated by the Stoics as a Kingdom governed by the Soul. According to Stoic principles these subjects cannot be separated one from the other, or from the other parts of philosophy; and therefore in treating each one we shall, as before, assume a general knowledge of all the others. The Stoics laid great stress upon the study of Physics, as the only sound basis for a scientific rule of human conduct; and some of them (beginning with Chrysippus), having especial regard to the elevated dignity of the study of Theology, were disposed to rank this branch of philosophy as the highest and last of its three principal divisions[2]. We shall however, in accordance with a view more generally held, reserve the last place for Ethics[3].

Fundamental Conceptions.

172. To the earlier Greek philosophers, as we have already seen, it appeared that a single bold intuition was enough, or almost enough, to discover a sufficient foundation upon which to construct a reasoned account of all things. Thus the Ionic philosophers took up as such a foundation one or more of the elements of air, fire, and water. But as soon as these three, together with earth, were recognized as ‘elements’ existing side by side, it became necessary to dig deeper, so as to secure a foundation for these as well. Thus Democritus resolved all four into ‘atoms’ and ‘void’; his theory was taken over by Epicurus, and remains to this day not only the most popular solution of the problem, but also that which (till quite recently) was tacitly assumed as the basis of all scientific investigation. Anaxagoras, working on different lines, began his account of the universe with ‘mind’ on the one hand and a primal conglomerate ‘matter’ on the other; a doctrine evidently based upon the popular dualism of soul and body, and still the basis of all transcendental philosophy and established religious conceptions. This Aristotle varied by assuming rather an ‘active’ and a ‘passive’ principle, force which works and matter upon which it works. Besides these conceptions many others need to be considered, which if not absolutely fundamental, are nevertheless matters of discussion in all philosophical schools, as those of motion, space, time, soul, body, God, the universe, cause, effect, will and necessity. In this way the original inquiry into the foundation of the universe developes into a general study of fundamental conceptions; and it is at this stage that it is taken over and dealt with by Stoicism, which adds to the list certain conceptions on which it lays a special stress and to which it gives a characteristic colour; such are those of ‘body,’ ‘spirit,’ and ‘tone.’

The Stoic monism.

173. The fact that the Stoics use from time to time the language of other schools or of popular speculation does not necessarily imply that this language is an adequate statement of their doctrine; and we frequently[4] find that the discussion of particular problems seems to be based on dualisms, though these are in the end subordinated to monistic statements. Thus in logic we have already noticed the sharp contrast between the perceiving mind and the external object of perception (αἰσθητόν, ὑπάρχον); nevertheless mind and object are ultimately declared to be akin[5]. So in particular the popular dualism of ‘soul’ and ‘body’ is often accepted by the Stoics, and yet as steadily superseded by the paradox that ‘soul is body.’ The reason given for this is that ‘body is that which acts and is acted upon[6]’; and this statement in the end overrides the Aristotelian distinction of force and matter, active principle and passive principle. ‘Body,’ as conceived by the Stoics, is the one ultimate element, the foundation and beginning of the universe; it contains within itself the capacity of action, and nothing but ‘body’ has this capacity. Body, and nothing but body, exists in the true sense; that certain other things have a quasi-existence (as we shall see later in this chapter) is an embarrassment which only brings into clearer relief this distinctive feature of the system. The Stoic ‘body,’ though it is also called ‘matter’ (ὕλη, materia), must not be confused with the ‘matter’ of modern philosophy, which has derived from Aristotle the implication of passivity[7]; much more closely it corresponds with the ‘stuff’ by which modern monistic philosophers denote the substratum of mind and body alike. To call the Stoics ‘materialists’ will generally prove misleading; it is the Epicurean system, to which the Stoics were sharply opposed, which (as we have seen)[8] corresponds to modern materialism.

The nature of ‘body.’

174. The conception of ‘body’ therefore replaces in the Stoic system the various elements which the Ionic philosophers assumed as the basis of the universe, and combines both parts of such dualistic elements as were assumed by Democritus, Anaxagoras and Aristotle. Since it is the foundation of all things it must be capable of taking very various shapes. In logic we have met with it under the name of the ‘substratum’ (τὸ ὑπάρχον, id quod est)[9], but it none the less includes the ‘subject’ or feeling and reasoning mind. In the universe as a whole it is ‘essence’ (οὐσία, essentia); in its parts it is ‘matter’ (ὕλη, silva)[10]; but it also appears, possessed of intelligence, as the deity[11], and again is identified with ‘breath’ or ‘spirit[12],’ and through this with the human soul[13]. Even in ethics it has its place; for all causes are bodily, and not least ‘the good’ and the respective virtues, all of which are bodies, for they act upon body[14]; similarly the emotions such as anger and melancholy, are of the nature of body[15].

Motion, space and time.

175. The Stoic ‘body’ in all its transformations is active and alert. It contains in itself the principle or power of movement; for though we observe that one body is set in motion by another, yet this could not be the case unless in the beginning there had been a body which had movement of itself[16]. As to the nature of the primal movement, the Stoics agree with Anaximenes that it may be described as alternate rarefaction and condensation. Rarefaction is a wave or ‘spirit’ spreading from the centre to the extremities; condensation is a contrary movement from the extremities to the centre[17]. The extension of body is ‘space,’ which therefore does not exist of itself, but only as a function of body[18]. Where there is no body (and body is limited), there is no space, but only the ‘boundless void’ beyond the universe[19]; of this we cannot say that it ‘exists’; rather it ‘not exists.’ Time also does not exist of itself, but only in the movement of body[20]. Neither space nor time existed before the universe, but have been all along bound up with it[21].