Nevertheless, we shall state, as far as the case admits, what is the nature of the Accident, and through what cause it is (τίς ἡ φύσις αὐτοῦ, καὶ διά τιν’ αἰτίαν ἐστίν· — 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 (ἡ τοῦ ὁπότερ’ ἔτυχεν — 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 τὸ ὁπότερ’ ἔτυχεν 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 — τὸ ποιητικόν (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.
Book Z.
We have already stated that Ens is a πολλαχῶς λεγόμενον — distinguished according to the ten figures or genera called Categories. The first is τί ἐστιν, or οὐσία (sensu dignissimo) — Essentia, Substantia (p. 1028, a. 15). The remaining Categories are all appendages of Essentia, presupposing it, and inseparable from it; whereas Essentia is separable from all of them, and stands first in reason, in cognition, and in time. All the other Categories are called Entia only because they are quantities, qualities, affections, &c., of this Essentia Prima. A man may even doubt whether they are Entia or Non-Entia, since none of them is either per se or separable. We ought hardly to say that a quality or an affection, enunciated abstractedly, is Ens at all — such as currere, sedere, sanitas: we ought more properly to say that currens equus, sedens homo, sanus miles, are Entia, enunciating along with the quality the definite Essence or Individual Substance to which it belongs (a. 24). The quality then becomes Ens, because the subject to which it belongs is an individual Ens (a. 27). Essentia Prima is first in reason or rational explanation (λόγῳ, a. 34), because in the rational explanation of each of the rest that of Essentia is implicated. It is first also in cognition, because we believe ourselves to know any thing fully, when we are able to answer Quid est? and say that it is homo or ignis; not simply when we are able to answer Quale or Quantum est? So that in answering the great and often-considered question, Quid est Ens? we shall first understand it as meaning Essentia (hoc sensu dignissimo), and shall try to solve it so (b. 3, περὶ τοῦ οὕτως ὄντος).
Essentia (understood in this sense) appears to belong in the most manifest manner to bodies: we predicate it of animals, plants, the parts thereof, the natural bodies such as fire, water, and such like, as well as the parts and aggregates thereof, such as the heaven and its parts, the stars, moon, and sun (p. 1028, b. 7-13). But are these the only Essences, or are there others besides? Or again, is it an error to call these Essences, and are all Essences really something different from these? This is a point to be examined. Some think that the limits of bodies (surface, line, point, monad) are Essences even more than the body and the solid: others admit no Essences at all beyond or apart from Percipienda; others again recognize other Essences distinct from and more eternal than the Percipienda; for example, Plato, who ranks Ideas or Forms, and the Mathematica, as two distinct Essences, while he places the Percipienda only third in the scale of Essence. Speusippus even enumerates a still greater number of Essences, beginning with the One, and proceeding to Numbers, Magnitudes, Soul, &c., with a distinct ἀρχή or principle for each (b. 21). Some others hold that Forms and Numbers have the same nature, and that there are other things coming near to these, such as lines and surfaces, in a descending scale to the Heaven and the Percipienda (b. 24). We must thus investigate which of these doctrines are true or false, whether there are any Essences beyond the Percipienda; and, if so, how they exist: whether there is any separable essence apart from Percipienda, and, if so, how and why; or whether there is nothing of the kind. But first we must give a vague outline what Essence is generally (ὑποτυπωσαμένοις, b. 31).