Euclid defines unity as that in virtue of which we call a thing one. This means to signify that unity precedes the unitary thing by nature, just as heat precedes the hot object. Plurality is the sum of ones, hence plurality cannot be prior to unity, from which it proceeds. Hence whatever plurality we find in our minds we know that unity precedes it; and even if it occurs to anyone that there is more than one creator, unity must after all precede them all. Hence God is one. This argument is strictly Neo-Platonic and is based upon the idealism of Plato, the notion that whatever reality or attributes particular things in our world of sense possess they owe to the real and eternal types of these realities and attributes in a higher and intelligible (using the term in contradistinction to sensible) world in which they participate. In so far as this conception is applied to the essences of things, it leads to the hypostatization of the class concepts or universals. Not the particular individual whom we perceive is the real man, but the typical man, the ideal man as the mind conceives him. He is not a concept but a real existent in the intelligible world. If we apply it also to qualities of things, we hypostatize the abstract quality. Heat becomes really distinct from the hot object, existence from the existent thing, goodness from the good person, unity from the one object. And a thing is existent and one and good, because it participates in Existence, Unity and Goodness. These are real entities, intelligible and not sensible, and they give to our world what reality it possesses. Plotinus improved upon Plato, and instead of leaving these Ideas as distinct and ultimate entities, he adopted the suggestion of Philo and gathered up all these intelligible existences in the lap of the universal Reason, as his ideas or thoughts. This universal Reason is in Philo the _Logos_, whose mode of existence is still ambiguous, and is rather to be understood as the divine mind. In Plotinus it is the first stage in the unfoldment of the Godhead, and is a distinct _hypostasis_, though not a person. In Christianity it is the second person in the Trinity, incarnated in Jesus. In Israeli, Gabirol and the other Jewish Neo-Platonists, it occupies the same place as the _Nous_ in Plotinus. In Bahya, whose taint of Neo-Platonism is not even skin deep, there is no universal Reason spoken of. But we do not really know what his ideas may have been on the subject, as he does not develop them in this direction. To return to Bahya's arguments in favor of the unity of God, we proceed to show that dualism would lead to absurd conclusions. Thus if there is more than one creator, they are either of the same substance or they are not. If they are, then the common substance is the real creator, and we have unity once more. If their substances are different, they are distinct, hence limited, finite, composite, and hence not eternal, which is absurd.