existence is necessary to account for all other existence; it has neither genus, species, nor differentia; it is both external and internal, at once apparent and concealed; it cannot be perceived by any faculty but is knowable by its attributes, and the best approach to knowledge is to know that it is inaccessible. In this treatment al-Farabi is mingling the teaching of philosophy proper with mysticism, in his days rapidly developing in Asiatic Islam, and especially in the Shi'ite community with which he was in contact. From the philosophical point of view God is unknowable but necessary, just as eternity and infinity are unknowable but necessary, because God is above all knowledge: but in another sense God is beneath all knowledge, as the ultimate reality must underlie all existing things, and every result is a manifesting of the cause.
The proof of the existence of God is founded upon the argument in Plato, Timaeus 28, and Aristotle, Metaphysics 12. 7, and was later on used by Albertus Magnus and others. In the first place a distinction is made between the possible, which may be only potential, and the real. For the possible to become real it is necessary that there should be an effective cause. The world is evidently composite, and so cannot itself be the first cause, for the first cause must be single and not multiple: therefore the world evidently proceeds from a cause other than itself. The immediate cause may itself be the result of another preceding cause, but the series of causes cannot be infinite, nor
