This dogma of universal determinism was combined in the Stoical system with an equally outspoken materialism. The capacity for either acting or being acted on was, according to Plato, the one convincing evidence of real existence; and he had endeavoured to prove that there is such a thing as mind apart from matter by its possession of this characteristic mark.[28] The Stoics simply reversed his argument. Whatever acts or is acted on, they said, must be corporeal; therefore the soul is a kind of body.[29] Here they only followed the common opinion of all philosophers who believed in an external world, except Plato and Aristotle, while to a certain extent anticipating the scientific automatism first taught in modern times by Spinoza, and simultaneously revived by various thinkers in our own day. To a certain extent only; for they did not recognise the independent reality of a consciousness in which the mechanical processes are either reflected, or represented under a different aspect. And they further gave their theory a somewhat grotesque expression by interpreting those qualities and attributes of things, which other materialists have been content to consider as belonging to matter, as themselves actual bodies. For instance, the virtues and vices were, according to them, so many gaseous currents by which the soul is penetrated and shaped—a materialistic rendering of Plato’s theory that qualities are distinct and independent substances.[30]
We must mention as an additional point of contrast between the Stoics and the subsequent schools which they most resembled, that while these look on the soul as inseparable from the body, and sharing its fortunes from first to last, although perfectly distinct from it in idea, they emphasised the antithesis between the two just as strongly as Plato, giving the soul an absolutely infinite power of self-assertion during our mortal life, and allowing it a continued, though not an immortal, existence after death.[31]
What has been said of the human soul applies equally to God, who is the soul of the world. He also is conceived under the form of a material but very subtle and all-penetrating element to which our souls are much more closely akin than to the coarse clay with which they are temporarily associated. And it was natural that the heavenly bodies, in whose composition the ethereal element seemed so visibly to predominate, should pass with the Stoics, as with Plato and Aristotle, for conscious beings inferior only in sacredness and majesty to the Supreme Ruler of all.[32] Thus, the philosophy which we are studying helps to prove the strength and endurance of the religious reaction to which Socrates first gave an argumentative expression, and by which he was ultimately hurried to his doom. We may even trace its increasing ascendency through the successive stages of the Naturalistic school. Prodicus simply identified the gods of polytheism with unconscious physical forces;[33] Antisthenes, while discarding local worship, believed, like Rousseau, in the existence of a single deity;[34] Zeno, or his successors, revived the whole pantheon, but associated it with a pure morality, and explained away its more offensive features by an elaborate system of allegorical interpretation.[35]