Because that which is finite is always bounded with reference to something... it is necessary that there should be no end... Number also appears to be infinite, and mathematical magnitudes, and that which is beyond the heavens. And since that which is beyond is infinite, body also appears to be infinite, and it would seem that there are infinite worlds; for why is there rather void here than there? ...If also there is a vacuum, and an infinite place, it is necessary that there should be an infinite body: for in things which have a perpetual subsistence, capacity differs nothing from being. The speculation of the infinite is, however, attended with doubt: for many impossibilities happen both to those who do not admit that it has a subsistence, and to those who do. ...It is ...especially the province of a natural philosopher to consider if there be a sensible infinite magnitude.

All those... who discourse concerning nature, always subject a certain other nature of... elements, to the infinite... But no one of those who make the elements to be finite introduces infinity. Such, however, as make infinite elements, as Anaxagoras and Democritus, say that the infinite is continuous by contact. ...Rationally, too, do all philosophers consider the infinite as a principle; for it cannot be in vain, nor can any other power be present with it than that of a principle: for all things are either the principle, or from the principle; but of the infinite there is no principle, since otherwise it would have an end. ...it is also unbegotten and uncorruptible, as being a certain principle: for... end is the corruption of everything. ...It likewise appears to comprehend and govern all things, as those assert who do not introduce other causes beside the infinite... It would seem also that this is divine: for it is immortal and indestructible, as Anaximander says, and most of the physiologists.

Since the science of nature is conversant with magnitudes, motion, and time, each of which must necessarily be either infinite or finite...we should speculate the infinite, and consider whether it is or not; and if it is what it is. ...All those who appear to have touched on a philosophy of this kind... consider it as a certain principle of beings. Some, indeed, as the Pythagoreans and Plato, consider it, per se, not as being an accident to any thing else, but as having an essential subsistence... the Pythagoreans... consider the infinite as subsisting in sensibles; for they do not make number to be separate; and they assert that what is beyond the heavens is infinite; but Plato says that beyond the heavens there is not any body, nor ideas, because these are no where: he affirms, however, that the infinite is both in sensibles, and in ideas. ...Plato establishes two infinities, viz. the great and the small.

There is... something which is in energy only; and there is something which is both in energy and capacity. ...of relatives, one is predicated as according to excess and defect: another according to the effective and passive, and, in short, the motive, and that which may be moved... Motion, however, has not a substance separate from things... But each of the categories subsists in a twofold manner in all things. Thus... one thing pertaining to it is form, and another privation. ...So the species of motion and mutation are as many as those of being. But since in every genus of things, there is that which is in entelecheia, and that which is in capacity; motion is the entelecheia of that which is in capacity... That there is energy, therefore, and that a thing then happens to be moved, when this energy exists, and neither prior nor posterior to it, is manifest. ... Neither motion nor mutation can be placed in any other genus; nor have those who have advanced a different opinion concerning it spoken rightly. ...for by some motion is said to be difference, inequality, and non-being; though it is not necessary that any of these should be moved... Neither is mutation into these, nor from these, rather than from their opposites. ...The cause, however, why motion appears to be indefinite, is because it can neither be simply referred to the capacity, nor to the energy of beings. ...It is difficult to apprehend what motion is: for it is necessary to refer it either to privation, or to capacity, or to simple energy; but it does not appear that it can be any of these. The above-mentioned mode, therfore remains, viz. that it is a certain energy; but... difficult to be perceived, but which may have a subsistence.

It is impossible for motion to subsist without place, and void, and time.

Since... nature is a principle of motion and mutation... it is necessary that we should not be ignorant of what motion is... But motion appears to belong to things continuous; and the infinite first presents itself to the view in that which is continuous. ...Frequently ...those who define the continuous, employ the nature or the infinite, as if that which is divisible to infinity is continuous.

Since causes are four in number, to know them all is the business of the natural philosopher, who also referring to the cause why a thing is to all of them, viz. to matter, form, that which moves, and for the sake of which a thing subsists, physically assigns a reason. Frequently, however, three of these causes pass into one: for the cause why a thing is, and that for the sake of which it is, are one. But that which motion first originates, is in species the same with these... There are three treatises; once concerning that which is immoveable; another concerning that which is moved, indeed, but is incorruptible; and a third concerning corruptible natures. So the cause of why a thing is, is assigned by him who refers to matter, to essence, and to the first mover... But there are two principles which are naturally motive; of which, one is not physical, because it does not contain in itself the principle of motion. And if there is any thing which moves without being moved, it is of this kind; as is that which is perfectly immoveable, that which is the first of all things, together with essence and form: for it is the end, and that for the sake of which a thing subsists. So that since nature is for the sake of something, it is also necessary to know this cause.

Fortune... and chance, are said to be in the number of causes... With some it is dubious whether these things have subsistence or not. For, say they, nothing is produced from fortune, but there is a definite cause of all such things... For if fortune were any thing, it would truly appear to be absurd; and some one might doubt why no one of the ancient wise men, when assigning the causes of generation and corruption, has ever defined any thing concerning fortune. ...Many things are produced, and have a subsistence, from fortune and chance... They did not, however, think that fortune was any thing belonging to friendship or strife, or fire, or intellect, or any thing else of things of this kind. They are chargeable, therefore, with absurdity, whether they did not conceive that it had a substance, or whether fancying that it had, they omitted it; especially since it was sometimes employed by them. Thus Empedocles says that the air...Thus it then chanc'd to run, tho' varying oft.He also says that the greater part of... animals were generated by fortune. But there are some who assign chance to the cause of this heaven, and of all mundane natures... We must consider... whether chance or fortune are the same... or different from each other, and how they fall into definite causes.

Let us consider, with respect to causes, what they are, and how many there are in number... this also must be done by us in discoursing concerning generation and corruption, and all physical mutation... knowing the principles of these...Cause... is after one manner said to be that, from which, being inherent, something is produced... But after another manner cause is form and paradigm (and this is the definition of the essence of a thing) and the genera of this. ...But it happens... that there are also many causes of the same thing, and this is not from accident. ...seed, a physician, he who consults, and, in short, he who makes, are all of them causes, as that whence the principle of mutation, or permanency, or motion is derived. ...It is, however, necessary always to investigate the supreme cause of every thing ...Further still, it is necessary to investigate the genera of genera; and the particulars of particulars... We should also explore the capacities of the capabilities, and the energizers of the things affected by energy.

According to one mode... nature is thus denominated, viz. the first subject matter to every thing which contains in itself the principle of motion and mutation. But after another mode it is denominated form, which subsists according to definition: for as art is called that which subsists according to art, and that which is artificial; so likewise nature is both called that which is according to nature, and that which is natural. ...that which is composed from these is not nature, but consists from nature; as, for instance, man. And this is nature in a greater degree than matter: for every thing is then said to be, when it is form in energy... entelecheia, rather than when it is incapacity.