The First Philosophy investigates the causes and principles of Entia quatenus Entia (p. 1025, b. 3). It is distinguished from other sciences, by applying to all Entia, and in so far as they are Entia; for each of the other sciences applies itself to some separate branch of Entia, and investigates the causes and principles of that branch exclusively. Each assumes either from data of perception, or avowedly by way of hypothesis, the portion or genus of Entia to which it applies; not investigating the entity thereof, but pre-supposing this process to have been already performed by Ontology: each then investigates the properties belonging per se to that genus (b. 13). It is plain that by such an induction not one of these sciences can demonstrate either the essence of its own separate genus, nor whether that genus has any real existence. Both these questions — both e? ?st?? and t? ?st?? — belong to Ontology (b. 18). (The belief derived from perception and induction never amounts to demonstration, as has been shown in the Analytica; you may always contest the universality of the conclusion—Alex. p. 734, b. 16, Br.)

Apart from Ontology, each of these separate sciences is either theoretical, or practical, or constructive (p. 1025, b. 21). Two of the separate sciences are theoretical — Physics and Mathematics; and, as Ontology (or Theology) is also theoretical, there are three varieties of theoretical science (p. 1026, a. 18).

Physical Science applies to subjects having in themselves the principle of mobility or change, and investigates, principally and for the most part, the Essence or Form thereof; yet not exclusively the Form, for the Form must always be joined with Matter. The subject of Physics includes Matter in its definition, like hollow-nosed, not like hollow (p. 1025, b. 33). All the animal and vegetable world is comprised therein; and even some soul, as far as soul is inseparable from Matter (pe?? ????? ???a? ?e???sa? t?? f?s????, ?s? ? ??e? t?? ???? ?st?? — p. 1026, a. 5).

Mathematics is another branch of theoretical science; applying to subjects immovable and in part inseparable from Matter; that is, separable from Matter only in logical conception (p. 1026, a. 7-15).

Theology, or First Philosophy, or Ontology, is conversant with subjects self-existent, immovable, and separable from Matter (p. 1026, a. 16).

Now all causes are necessarily eternal; but these more than any other, because they are the causes active among the visible divine bodies; for, clearly, if the Divinity has any place, it must be found among subjects of that nature; and the most venerable science must deal with the most venerable subjects (p. 1026, a. 19). The theoretical sciences are more worthy than the rest (a??et?te?a?), and First Philosophy is the most worthy among the theoretical sciences (a. 22). A man may indeed doubt whether First Philosophy is distinguished from the other theoretical sciences by being more universal, and by comprehending them all as branches; or whether it has a separate department of its own, but more venerable than the others; as we see that Mathematics, as a whole, comprehends Geometry and Astronomy (a. 27). If there exist no other distinct Essence beyond the compounds of Nature (pa?? t?? f?se? s??est????a? — a. 28), Physics would be the first of all sciences. But if there be a distinct immovable Essence, that is first; accordingly the science which deals with it is first, and, as being first, is for that reason universal (?a? ?a????? ??t?? ?t? p??t? — a. 30). It is the province of this First Philosophy to theorize respecting Ens qu Ens — what it is and what are its properties qu Ens (a. 32). (Alexander says the First Philosophy is more universal than the rest, but does not comprehend the rest: p??t? p??t?? ?a? ?a????? ?? p??? t?? ???a?, ?? pe??????sa ??e??a?, ???’ ?? p??t? — Schol. p. 736, a. 27.)

Now Ens has many different meanings:—

1. Ens ?at? s?e????.

2. Ens ?? ?????? — Non-Ens ?? ?e?d??.

3. Ens ?at? t? s??ata t?? ?at?????a? (decuple).

4. Ens d???e? ?a? ??e??e??.

1. Respecting the first, there can be no philosophical speculation (p. 1026, b. 3). No science, either theoretical, or practical, or constructive, investigates Accidents. He who constructs a house, does not construct all the accidents or concomitants of the house; for these are endless and indeterminate. It may be agreeable to one man, hurtful to a second, profitable to a third, and something different in relation to every different Ens; but the constructive art called house-building is not constructive of any one among these concomitants (b. 7-10). Nor does the geometer investigate the analogous concomitants belonging to his figures; it is no part of his province to determine whether a triangle is different from a triangle having two right angles (b. 12). This is easy to understand: the Concomitant is little more than a name — as it were, a name and nothing beyond (b. 13). Plato came near the truth when he declared that Sophistic was busied about Non-Ens; for the debates of the Sophists turn principally upon Accidents or Concomitants, such as, Whether musical and literary be the same or different? Whether Koriskus or literary Koriskus, be the same or different? Whether everything which now is, but has not always been, has become; as in the case of a man who being musical has become literary or being literary has become musical? and such like debates (see Alexander, Schol. p. 736, b. 40). For the Concomitant or Accident appears something next door to Non-Ens (????? t? t?? ? ??t??, p. 1026, b. 21), as we may see by these debates. Of other Entia there is generation or destruction, but of Accidents there is none (b. 23).

Nevertheless, we shall state, as far as the case admits, what is the nature of the Accident, and through what cause it is (t?? ? f?s?? a?t??, ?a? d?? t??’ a?t?a? ?st??· — p. 1026, b. 25): we shall perhaps at the same time explain why there can be no science respecting it. Among Entia, some are always and necessarily the same, others are usually but not always the same. These which come to pass in neither of these two ways, are called Accidents or Concomitants. Of the first two, the Constant and the Usual, there is always some definite cause; of the third, or Accidents, there is none: the cause of these is an Accident (p. 1027, a. 8). In fact, Matter is the cause of Accidents, admitting as it does of being modified in a way different from the usual and ordinary way (a. 13). It is plain that there can be neither science nor teaching of Accidents: the teacher can teach only what is constant or usual, and nothing beyond (a. 20).

Now of these Accidents, there is a certain principle or cause which it is indispensable to admit — Chance (? t?? ?p?te?’ ?t??e? — p. 1027, b. 12). There must be principles and causes, generable and destructible, yet which never are either generated or destroyed; if this were not so, all events would occur by necessity (p. 1026, b. 29-31). (Thus the builder, considered as cause of the house which he builds, has been generated, i.e., he has acquired the art of building and the proper accessories; and he will be destroyed, i.e., he will lose his art, and its conditions of being exercised. But, considered as the cause of the accidents belonging to the house, of its being annoying or inconvenient to A or B, he has not been generated nor will he be destroyed; i.e., he has neither acquired, nor will he lose, any skill or conditions tending to the production of this effect. As the contact of two substances is not generated, but appears of itself along with the substances when they are generated; as the limits of periods of time appear without generation along with the periods of time themselves; so the builder, when he acquires the power of building the house, stands possessed thereby, without any additional time or special generation, of the power to produce the concomitant accidents of the house. The house is thus produced by necessity; its concomitant accidents not by necessity — Alex. Schol. p. 738, a. 19-33.)

But whether this t? ?p?te?’ ?t??e? is to be considered as referable to Matter, End, or Movent, is a point important to be determined (p. 1027, b. 15). Aristotle shows elsewhere that it is referable to the last of the three — t? p???t???? (Asklepius, p. 738, b. 41).

Having now said enough upon Ens per Accidens, we proceed to touch upon the second variety of Ens — Ens as the True, Non-Ens as the False.

This variety of Ens depends upon conjunction and disjunction, and forms an aggregate of two portions separately exhibited and brought together in the Antiphasis. Such conjunction and disjunction is not in things themselves; but in the act of intelligence which thinks the two things together and not successively: in regard to simple matters and Essence, not even any special conjoining act of intelligence is required; such things must be conceived together, or not conceived at all (p. 1027, b. 27). The mental act of apprehension, in these cases, is one and indivisible: you either have it entire at once, or not at all.

The cause of this variety of Ens is to be found in a certain affection of the intelligence; that of the preceding variety of Ens is an undefined or indeterminate cause (b. 34). Both these two varieties of Ens are peculiar, standing apart from what is most properly and par excellence Ens, i.e., from the Ens according to the ten Categories, on which we shall now say something.