=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.’ [Sidenote: The Stoic monism.]