Introduction

In order to be able to place the present Essay in an appropriate context the reader should consult :

• The Essay on Substance and Accident.
• The following section of the Essay What is an individuum Part 2.

The Thomistic view about the Analogy of Being with respect to Substance and Accident, seen from the Accident

In this text, but also in all other Thomistic texts, the existence (i.e. reality) of an ontological distinction between "Substance" and "Accident" is already presupposed, not demonstrated. Our experience appears to suggest this distinction, which has then been built into our language (through experience and thinking). The detection (or presumed detection) of such a substance-accident structure is also promoted (i.e. suggested) by experiencing our own individuality (being an individual). We seem to experience that in our individuality something remains the same under changing conditions. Whether really something remains exactly the same, and what it precisely is, that remains the same, is not, or hardly, investigated in the Thomistic texts. There especially the status of the generic or specific proprium as proprium accidens is problematic.

REMARK : A proprium is a necessary property of something. But because it is a property, it is ontologically not independent, it cannot exist on its own. And when it is such a property -- a necessary property -- of a substance, it is a proprium accidens, i.e. something, not, it is true, immediately belonging to the Essence of a substance, but nonetheless in some way implied by that Essence, and accordingly always accompanying that Essence. As such it is (just) a diagnostic feature. A classical example of such a proprium accidens is "THE ABILITY TO LAUGH", with respect to the human species. This feature is always present in every human being, and is absent elsewhere. Because of this it is evident that this feature stems in some way from the Essence of man, but it cannot exist on its own accord. If such a feature, like the example just given, is limited to the members of a species, then we have to do with a specific proprium , but if it is limited to the members of a genus, then we have to do with a generic proprium.

The status of this proprium accidens is problematic because in this case we have to do with a feature that does not change (is not substituted) under the constancy of something else, as a real accidens is supposed to do. The feature is permanent but nonetheless considered by Classical Metaphysics as an accident. The Essence is also permanent (as long as the thing itself exists). So why then is, say, "THE ABILITY TO LAUGH" an accident? Not, it seems, because it is substitutable, because it isn't. So the reason must be that "THE ABILITY TO LAUGH" is not ontologically independent. But what about "THE ABILITY TO THINK RATIONALLY"? In Classical Metaphysics this feature is considered not to be an accident, not something that is ontologically dependent. But why? What is the difference between "THE ABILITY TO LAUGH" and "THE ABILITY TO THINK RATIONALLY"?

The considerations in the relevant text of De Ente et Essentia are again strongly oriented towards (the example of) man. And therefore it is perhaps not guaranteed that the considerations are sufficiently general, when the status of, say, an accident is concerned.
In the ensuing text we therefore will meet many things which are not investigated, but presupposed.

From De Ente et Essentia, Chapter 6, line 1--109.
I make use of the translation by Robert T. Miller (who owns the copyright) from the Internet (See for links the beginning of the first Essay of this Classical Series.

The text will be supplied with several comments, placed between square brackets [....].

"We should now see in what way there are essences in accidents, having said already how essences are found in all types of substances. Now, since, as said above, the essence is that which is signified by the definition, accidents will thus have essences in the same way in which they have definitions. But accidents have incomplete definitions, because they cannot be defined unless we put a subject in their definitions, and this is because they do not have absolute existence per se apart from a subject, but just as from the form and the matter substantial existence results when a substance is compounded, so too from the accident and the subject does accidental existence result when the accident comes to the subject. Thus, neither the substantial form nor the matter has a complete essence, for even in the definition of the substantial form we place something of which it is the form, and so its definition involves the addition of something that is beyond its genus, just as with the definition of an accidental form. Hence, the natural philosopher places the body in the definition of the soul because he considers the soul only insofar as it is the form of the physical body.

But this is the case only with substantial and accidental forms because, just as the substantial form has no absolute existence per se without that to which the form comes, so too does that to which the form comes, namely matter, have no absolute per se existence. Thus, from the conjunction of both there results that existence in which the thing per se subsists, and from these two there is made one thing per se; for, from the conjunction of these there results a certain essence. Hence, although considered in itself the form does not have the complete aspect of an essence, nevertheless it is part of a complete essence. But that to which an accident comes is in itself a complete being subsisting in its own existence, and this existence naturally precedes the accident that supervenes. Therefore, the supervening accident, from its conjunction with the thing to which it comes, does not cause that existence in which the thing subsists, the existence through which the thing is a being per se; it causes, rather, a certain secondary existence without which the subsisting being can be understood to exist, as what is first can be understood without what is second. Hence, from the accident and the subject there is made something that is one accidentally, not essentially; and so from the conjunction of these two there does not result an essence, as there does from the conjunction of form and matter. And so an accident has neither the aspect of a complete essence nor is it a part of an essence; rather, just as an accident is a being only in a certain sense, so too does it have an essence only in a certain sense.

But since that which is greatest and truest in a genus is the cause of the lesser things in the genus (as fire, which is at the extreme of heat, is the cause of heat in other hot things, as the Philosopher says in II Metaphysicae cap. 1 (993b24-27)), thus substance, which is first in the genus of beings and which has essence in the truest and greatest way, is the cause of accidents, which participate in the notion of being only secondarily and in a certain sense. But this happens in a variety of ways. Since the parts of substance are matter and form, certain accidents are principally a consequence of form, and certain accidents are principally a consequence of matter. Now, while we find some forms, like the intellectual soul, whose existence does not depend on matter, matter does not have existence except through form. Hence, among those accidents that are a consequence of form, there are some that have no communication with matter, such as understanding, which does not take place through a corporeal organ, as the Philosopher proves in III De Anima cap. 1 (429a18-b5). Other accidents that are a consequence of form do have communication with matter, and among these is sensation. But no accident a consequence of matter is without some communication with form.

Among the accidents that are consequences of matter there is found a certain diversity. Some accidents follow from the order the matter has to a special form, as the masculine and the feminine in animals, the difference between which is reduced to the matter, as the Philosopher says in X Metaphysicae cap. 9 (1058b21-23). Hence, the form of the animal having been removed, these accidents do not remain except in some equivocal sense.

[ This phenomenon of the masculine and the feminine with respect to individuals of animals (with distinguished sexes) and also plants (with distinguished sexes) can perhaps be compared with the phenomenon of enantiomorphy with respect to some species of crystals. These are crystal species that come in two variaties, that only differ from each other with respect to their 'handedness'. They are like two hands of a same person : mirror images of each other.
MASCULINITY is a condition in which a certain substance can find itself. For an individual substance this condition (state) (masculine or feminine) is permanent (except certain snails). Within the species masculine (or feminine) is not permanent, but varies from individual to individual. Because this character varies within the species we know (1) that this character cannot exclusively depend on the Form, but on Matter as well (albeit always through (an aspect of) the Form. This, because the causation of an accident can never be accomplished by matter alone) and (2) (we not only know) that masculine (or feminine) is a predicamental accident, but (we know) also that it is not a proprium accidens. ]

Other accidents follow from the order the matter has to a general form, and so with these accidents, if the special form is removed, the accidents still remain in the thing, as the blackness of the skin of an Ethiopian comes from the mixture of the elements and not from the notion of the soul, and hence the blackness remains in the man after death.

Since everything is individuated by matter and is placed in its genus or species through its form, the accidents that follow from the matter are accidents of the individual, and by these accidents individuals of the same species differ one from another. But the accidents that follow from the form are properly passions of the genus or species, and so they are found in all things participating in the nature of the genus or species, as risibility in man follows from the form, for laughter comes from a certain kind of understanding in the soul of man.

[ Here St Thomas expounds the specific and generic propria. These originate from the specific, repectively, generic form and therefore are constant within respectively the species and the genus. And if they indeed originate per se from those forms, then they cannot occur in the absence of those forms (Thus not in other species, respectively genera, because if that would be the case, then they would apparently originate from a more general form). Of course we could imagine that a certain accident (thus a certain phenomenon) could have several causes, and so could originate from a form A, but also from a form B, and, to be sure, not by virtue of something that is commonly possessed by these forms. Nevertheless this does not appear to be very probable : It appears evident that the effect must be somewhat different in both cases.
St Thomas also speaks about accidents that originate from matter (always through the substantial form). And because, so he says, matter is the principle of individuation, these accidents belong to the individual (as individual). Because these accidents follow from the matter of the relevant individual, they must be constant for that individual, because in fact they originate from the individual (substantial) form (because matter can only generate something through its form). And so we have the individual propria. These are characteristics that always accompany that individual, and that do not occur in other individuals, like the faces and certain traits of character in human individuals.
The accidents under consideration (The individual propria, specific propria, generic propria) are caused by their subject (their substrate), either by the form, or by the matter-through-the-form). Because the subject in a certain sense exists outside the accident (which exists in that subject), i.e. not belonging to its proper essence ( ratio propria ), that subject is the extrinsic cause of those accidents.
There are however also accidents whose causes lie totally outside the relevant composite (But the subject is always the material cause of the accident). These are all the conditions (states) (in a more strict sense) in which the thing can happen to find itself (i.e. under which the thing happens to be), like for instance the phenomenon of having become tanned by the sun. These conditions are very diverse indeed, and they vary already within the individual's existence. ]

We should also note that some accidents are caused by the essential principles of a thing according to its perfect act, as heat in fire, which is always hot, while other accidents are the result of an aptitude in the substance, and in such cases the complete accident arises from an exterior agent, as transparency in air, which is completed through an exterior luminescent body. In such things, the aptitude is an inseparable accident, but the complement, which comes from some principle that is beyond the essence of the thing, or that does not enter into the constitution of the thing, is separable, as the ability to be moved, and so on."

[ Here St Thomas expounds that an ability or aptitude can be permanent, while the corresponding actions and phenomena (made possible by those aptitudes) are not permanent. In fact all this relates, among other things, to the difference between the ability to laugh (risibility) and (the act of) laughing. LAUGHING has as its material cause the substance, i.e. the subject of the accident "to be in the condition of laughing". More precisely determined this material cause is the substantial form of this subject (this also applies to "the ability to laugh"), but (and this does not also apply to "the ability to laugh") "laughing" has also a cause that lies totally outside the individual composite (This cause is the efficient cause). Even when we have to laugh about what we are thinking, then this thinking will, directly or indirectly, always refer to something extramental that has happened, and this then is the ultimate efficient cause of that laughing.
Would it be possible to interpret "the ability to think" as a proprium accidens of man, just like "the ability to laugh"? Is then "the ability to think", i.e. (something) being rational, an accident with respect to man? At least "thinking" is an accident, because a human individual does not think constantly (for instance not in the dreamless part of sleep). ]

In Chapter 6 of De Ente et Essentia line 110--128 St Thomas treats of the subsuming of an accident under a Predicament.
A Predicament (or Category) is one of the ten most general whatnesses, or ways of being, of something (See here, in the Essay on Substance and Accident). Such a Predicament is a highest genus, terminating a certain series of genera with increasing generality, for instance, the following three series, leading up to the predicaments SUBSTANCE, QUALITY, QUANTITY, respectively :

In order to be placed into a predicament (and consequently to define, and thus to know), the item in question must have one homogeneous nature, i.e. it should have ONE determined nature, or to be ONE determined nature.
Well, a composite of matter and substantial form, is such a per se unity, probably because matter and substantial form are interdependent. So such a composite can be placed into a predicament. On the other hand, a substance-accidens composite is -- according to St Thomas -- not such a per se unity (at most, in some cases, a per se 2nd mode unity, namely there where an accident necessarily follows upon the substance in which it is). A substance-accident composite is an accidental unity, although however also in this case the accident depends upon the substance in which it resides, and the substance cannot exist without accidents (at least in a non-theological context). The substance-accident composite is accordingly not a per se unity just like that, and therefore it is not one determined nature, and that's why it cannot, just like that, be placed into a predicament, surely not when the accident is expressed concretely, like "white" (in contrast to "whiteness"), because in that case the subject is co-signified ("white" means : that something that has whiteness), and then we have something that is not a unity. An accident cannot be placed into a predicament until it is expressed abstractly, as with the term "whiteness", because only then we have to do with one determined nature.
What now would be the difference between :
The dependency of prime matter on one or another substantial form, and
The dependency of substance (here the composite of matter and substantial form) on one or another (or more) accidental form(s)?
In both cases we have to do with a substrate that should be 'formed-over' (and only then it is (a substrate)).
With respect to substitutable accidents it is evident that their substance is not dependent upon such an accident, because otherwise the accident would never be substituted by another, it would be permanently present in order to guarantee the permanent presence of the substance. Perhaps better expressed: If the substance would be dependent upon such a varying (i.e. more or less constantly being replaced by another) accident, then this substance would vary itself, it would vary together with the accident.
But substance is assumed not to vary, i.e. not to vary when accidents are being replaced by others.
But with respect to permanent accidents, such a dependency (i.e. the dependency of the substance upon such an accident) would be reasonable, i.e. cannot be a priori excluded as a possibility. In the Scholastic writings one identifies the cause of the permanency of such an accident not with the dependence of the substance upon that accident, in which case that 'accident' could in fact be seen as an essential part of the substance, but the other way around, namely the dependency of that (given) accident upon that (given) substance : That substance causes this accident necessarily, and because of that it would be present permanently. In this case the accidental nature (i.e. to be an accident, and not an essential part, but a derived part) is stipulated, not demonstrated.
So while the dependency in the case of prime matter is always (considered as) a dependency of the substrate upon the form, in the case of substance (as substrate) that dependency is considered to be always a dependency of the form (accident) upon the substrate, although in the case of permanent accidents the reverse cannot be excluded beforehand.