But in this discussion of Plato’s religious philosophy we have left one important subject untouched—the problem of evil. This was a question which a mind so acute and inquisitive as Plato’s could not finally avoid. Of the presence of evil in the world he was fully aware, and indeed he maintained that evils must always exist, for there must remain something antagonistic to the good; and since evils cannot exist in heaven the earth is their abode, from which man must try to escape.[208] On the source of evil, however, he touches only in the Statesman and the Timaeus;[209] in both the question is intimately connected with his theories of creation, which he sets forth in myth. But leaving aside the Platonic imagery, I will simply remind you that earlier in this lecture we saw that Plato conceived the world we know as dual—the phenomenal world known through the senses and the world of ideas apprehended by reason. Now the ideas alone have Being; but the phenomenal world is always in a state of Becoming, that is, of coming into being and of ceasing to be; it is both temporal and imperfect. Obviously there must be some principle, parallel in a way to the perfect and eternal ideas, such that it can receive them, and by its participation in them bring the imperfect sensible world into transitory existence. This principle is to Plato the material element. Now since he ascribes to the ideas alone real existence, that is, Being, the material principle must be Not-being. It is the negative substratum of all sensible phenomena, itself invisible, without form or characteristic, or in Plato’s words “the receptacle, and in a manner, the nurse of all generation” for, although itself formless, it is capable of taking on all the forms which the ideas may impose upon it. Plato himself could not avoid the difficulties which such a material substratum raises, and at times he is forced to speak as if it were something real in itself, having an existence beside the ideas. But his true notion seems to be that matter is mere negation, like the Aristotelian στέρησις, something which cannot be grasped by the intellect, as can the ideas, or perceived by the senses, as can the phenomenal world; it is identical with space. Of course when Plato talks about this negative principle, he inevitably speaks as if we could know something about it.[210]