Aquinas: On Being and Essence - Chapter 6

Chapter Six

ESSENCE AS FOUND IN ACCIDENTS

[1] Now that we have explained how essence is present in all substances, it remains for us to see how essence exists in accidents. Because essence is what the definition signifies, as has been said,†1 accidents must have an essence in the same way that they have a definition. Now their definition is incomplete, because they cannot be defined without including a subject in their definition.†2 This is because they do not have being in themselves, independent of a subject; as substantial being results from form and matter when they come together, so accidental being results from an accident and a subject when the former comes to the latter. For the same reason neither a substantial form nor matter has a complete essence, because the definition of a substantial form must include the subject of the form. It is defined, therefore, by adding something outside its genus, just like the definition of an accidental form. That is also why the body is included in the definition of the soul when it is defined by the natural philosopher, who considers the soul only as the form of a physical body.

[2] There is a considerable difference, however, between substantial and accidental forms. As a substantial form does not have being in itself, independent of that to which it is united, so neither does the matter to which it is joined. From their union results that being in which the reality subsists in itself, and from them is produced something essentially one. An essence, therefore, results from their union. It follows that although a form, considered in itself, does not have the complete nature of an essence, nevertheless it is part of a complete essence. But that to which an accident is added is a complete being in itself, subsisting in its own being; and this being is by nature prior to the supervening accident. That is why the supervening accident, by its union with the subject to which it comes, does not cause that being in which the reality subsists, and through which the reality is a being in itself. Rather, it causes a secondary being, without which we can conceive the subsistent reality to exist, as what is primary can be understood without what is secondary. So the accident and its subject do not produce something essentially, but accidentally, one. This explains why their union does not result in an essence, like the conjunction of form and matter. It also explains why an accident neither has the nature of a complete essence nor is part of a complete essence. As it is a being in a qualified sense, so it has an essence in a qualified sense.†3

[3] Furthermore, that which is said to be most fully and truly in a genus is the cause of everything posterior in the genus. For example, fire, which is the ultimate in heat, is the cause of heat in hot things, as the Metaphysics says.†4 That is why substance, which holds the first place in the genus of being, having essence most truly and fully, must be the cause of accidents, which share the nature of being secondarily and in a qualified sense.

[4] This happens in different ways. The parts of substance being matter and form, some accidents result principally from form and others from matter.†5 There is a form whose being does not depend on matter (for example, the intellectual soul),†6 whereas matter has being only through form. That is why among accidents that result from form there are some that have nothing in common with matter, as for example understanding, which does not take place through a bodily organ, as the Philosopher proves.†7 On the contrary, other accidents deriving from form do have something in common with matter, as for example sensation and the like. But no accident results from matter without having something in common with form.

[5] Among accidents that derive from matter we find the following difference. Some accidents result from matter because of its relation to a special form. Examples are male and female among animals--a difference that is reducible to matter, as the Metaphysics says.†8 That is why, once the form of animal has been removed, these accidents no longer remain except in an equivocal sense. Other accidents result from matter in its relation to a general form. In this case, when the special form is taken away, these accidents still remain in the matter. An example is the blackness of an Ethiopian's skin, which comes from the mixture of the elements and not from the nature of the soul, with the result that it remains in him after death.

[6] Because everything is individuated by matter and located in a genus or species through its form, accidents that derive from matter are accidents of the individual and they differentiate individuals within the same species. On the contrary, accidents that result from the form are properties belonging to the genus or species, and consequently they are found in everything sharing the nature of the genus or species. For example, the ability to laugh results from man's form, for laughter occurs because of some perception on the part of the human soul.

[7] Another point to notice is that accidents are sometimes caused in perfect actuality by the essential principles, like heat in fire, which is always actually hot. But sometimes accidents are caused only as aptitudes, and they are completed by an external agent, like transparency in the air, which is complemented by an external luminous body.†9 In cases like these the aptitude is an inseparable accident, whereas the completion that comes from a source external to the essence of the thing, or that does not enter into its constitution, will be separable from it, like movement and other accidents of this kind.

[8] Still another fact worthy of notice is that genus, species, and difference are derived differently in accidents and in substances. In substances, from substantial form and matter there is constituted something essentially one, the consequence of their union being one nature that is properly in the category of substance. That is why, in the case of substances, concrete names that signify the composite are properly said to be in a category, either as a species or as a genus, as for example 'man' or 'animal'. Form or matter, on the contrary, is not in a category in this way but only by reduction, as principles are said to be in a category.†10 From an accident and its subject, however, there is not produced something essentially one. Hence the result of their union is not one nature to which the notion of genus or species can be attributed. That is why terms designating accidents concretely, like 'something white' or 'something musical', cannot be placed in a category except by reduction. They are in a category only when expressed abstractly, like 'whiteness' or 'music'.

[9] Because accidents are not composed of matter and form, we cannot take their genus from matter and their difference from form, as we do in composite substances. Rather, we must take their primary genus from their mode of being, because the term 'a being' is predicated in diverse ways, by priority and posteriority, of the ten genera of the categories.†11 For example, quantity is called a being because it is the measure of substance, quality because it is the disposition of substance, and so on with the other accidents, as the Philosopher says.†12 Their differences, however, are derived from the diversity of the principles that cause them. And because properties result from the specific principles of the subject, this subject takes the place of the difference in their definition when they are defined in the abstract, which is the way they are properly in a category. For instance, we say that snubness is a curvature of the nose. But the converse would be true if we defined them in the concrete. In this case the subject would be placed in their definition as the genus, because these accidents would then be defined like composite substances, in which the concept of the genus is derived from matter. An example is calling a snub nose a curved nose. The same is true when one accident is the principle of another, as action, passion, and quantity are principles of relation. (That is why the Philosopher divides relation with reference to these in the Metaphysics).†13 But because the specific principles of accidents are not always evident, we sometimes take the differences of accidents from their effects, as when we say that colors are differentiated as 'dilating' and 'expanding'--differences that are caused by the abundance and scarcity of light, which produce the different species of color.†14

[10] It is clear, then, how essence exists in substances and in accidents, and in composite and simple substances. It is also evident how the universal concepts of logic are related to all these, with the exception of the first cause, which is absolutely simple. Because of its simplicity, neither the notion of genus nor of species, nor consequently the notion of definition, applies to it. In this being may our treatise find its end and fulfillment.

Amen