Arguments for eternity composed a particularly important area of philosophical debate among Greek, Jewish, Islamic, and Christian philosophers during the ancient and medieval periods. The foremost philosopher arguing for eternity was Aristotle. Those ascribing to Creationism ex nihilo (that is, creation from nothing) challenged these arguments for eternity, and held instead that God created the universe, so that the universe had a definite beginning in time.
Everything that comes into existence does so from a substratum. If the underlying matter of the universe came into existence, it would come into existence from a substratum. But the nature of matter is precisely to be the substratum from which other things arise. Consequently, the underlying matter of the universe could have come into evidence only from an already existing matter exactly like itself; to assume that the underlying matter of the universe came into existence would require assuming that an underlying matter already existed. The assumption is thus self-contradictory, and matter must be eternal.
The key premise of the argument is, clearly, that everything that comes into existence does so from a substratum. Aristotle defends this argument inductively as follows:
Maimonides challenged the inductive assertion on that "everything in existence comes from a substratum," on that basis that his reliance on induction and analogy is a fundamentally flawed means of explaining unobserved phenomenon. According to Maimonides, to argue that "because I have never observed something coming into existence without coming from a substratum it cannot occur" is equivalent to arguing that "because I cannot empirically observe eternity it does not exist."
Prior to a thing's coming into actual existence, its existence must have been 'possible.' Were its existence necessary, the thing would already have existed, and were its existence impossible, the thing would never exist. The possibility of the thing must therefore in some sense have its own existence. Possibility cannot exist in itself, but must reside within a subject. If an already existent matter must precede everything coming into existence, clearly nothing, including matter, can come into existence ex nihilo, that is, from absolute nothingness. An absolute beginning of the existence of matter is therefore impossible.
The argument is challenged on the basis that the "possibility" of creation could be ascribed to the Creator, and on the basis that the concept of "possibility" is merely an intellectual judgment with no actual existence in any real sense.
Aristotle argues that option A is self-contradictory because an object cannot move before it comes into existence, and the act of coming into existence is itself a "movement," so that the first movement requires a movement before it, that is, the act of coming into existence. (Aristotle fails, however, to explain why the act of coming into existence could not have been the required first movement, in which case this option is not self-contradictory).
Aristotle argues that option B is unsatisfactory for two reasons.
Aristotle concludes that motion is necessarily eternal.
Creationists responded that the "First motion" could be ascribed to God's creative act (which would, of course, be transcendental and thus not necessarily physical in nature).
Creationists responded that the apparent contradiction is only in our imaginations, as the perceived necessity as time "before" time is merely due to our experience, and not anything essential about the universe. God could be beyond time, but the universe exhibit a definite beginning and ending of time.
One philosophical critique of the Creationist argument counters that, no one can say, write, figure, argue or demonstrate in anyway what the notion that God exists outside or beyond time means or what properties and qualities such an existence has. This is because the concept transcends all thinking. If such a concept transcends all thinking no reason logical or illogical can be given and we therefore cannot be responsible for knowing it. Thus, even if God exists outside or beyond time (and has power such that God can create and sustain contradictions) we cannot have reason to believe such a claim and it remains as plausible as any belief whatever. Some have countered this argument saying that reason is not required for true belief. In this case, one can still reasonably believe anything giving all belief without reason no value.
Creationists responded that God created the dimensions at the same time he created the matter, so there was no vacuum before there was matter.