Maimonides criticizes the theory of the Eternity of the Universe on the grounds that it is not possible to find out how a system came about by examining its properties in its current condition, because the scientific principles that govern the sustained existence of a system need not be the same as those which govern the genesis or destruction of that system.

For example, human beings possess organs which work together in a careful balance; by examining a human being, it is not possible to conceive how a zygote could turn into an embryo and how a clump of cells can grow into a fully-formed human being. He illustrates this by giving the example of a male child who lost his mother at a young age and was brought up by his father in an isolated island where there were no women. If this child wanted to know how he came into the world, the whole process of fertilization, gestation, and childbirth would seem incredulous to him because, on examining a fully-developed human being, it seems unlikely that it is possible for a human to grow in the belly of another human being and to survive, suspended inside a liquid, for months. “It is therefore quite impossible to infer from the nature which a thing possesses after having passed through all stages of its development, what the condition of the thing has been in the moment when this process commenced”.

Thus, any objections to the theory of Creation must — says Maimonides — rely on something other than its present properties. Because its present properties tell us nothing about how it came about. This rules out those proofs for the eternity of the Universe attributed to Aristotelians in chapter 14 which rely on the present properties of the Universe, because “We admit the existence of these properties, but hold that they are by no means the same as those which the things possessed in the moment of their production”.

In short, the properties of things when fully developed contain no clue as to what have been the properties of the things before their perfection. … For the state of the whole Universe when it came into existence may be compared with that of animals when their existence begins; the heart evidently precedes the testicles, the veins are in existence before the bones; although, when the animal is fully developed, none of the parts is missing which is essential to its existence.

This argument is key to Maimonides’ project of upholding his religious beliefs to philosophical scrutiny. He emphasizes this to the reader by saying that this idea — that “the properties of things when fully developed contain no clue” about how they were developed “is a high rampart erected round the Law, and able to resist all missiles directed against it.”

At this stage, Maimonides does not believe he has established the theory of Creation from a scientific perspective. Instead,

we do not desire to prove the Creation, but only its possibility: and this possibility is not refuted by arguments based on the nature of the present Universe, which we do not dispute. When we have established the admissibility of our theory, we shall then show its superiority. In attempting to prove the inadmissibility of Creatio ex nihilo, the Aristotelians can therefore not derive any support from the nature of the Universe; they must resort to the notion our mind has formed of God (ليس من طبيعة الوجود بل مما يقضيه العقل في حق الإله).