1. A small mistake in the beginning is a big one in the end, according to the Philosopher in the first book of On the Heavens and the Earth. And as Ibn-Sînâ says in the beginning of his Metaphysics, being and essence are what is first conceived by the intellect.

2. Thus, to avoid making mistakes out of ignorance of them, and to become familiar with the difficulties they entail, we must point out what is signified by the words “being” and “essence,” and how they are found in diverse things, and how they are related to the logical intentions, genus, species, and difference.

3. Since we ought to acquire knowledge of what is simple from what is composed, and come to what is prior from what is posterior, so that, beginning with what is easier, we may progress more suitably in learning; we ought proceed from the meaning of the word “being” to that of the word “essence.”

4. We should notice, therefore, that the word “being,” taken without qualifiers, has two uses, as the Philosopher says in the fifth book of the Metaphysics. (1) In one way, it is used apropos of what is divided into the ten genera; (2) in another way, it is used to signify the truth of propositions. The difference between the two is that in the second way everything about which we can form an affirmative proposition can be called a being, even though it posits nothing in reality. It is in this way that privations and negations are called beings; for we say that affirmation is opposed to negation, and that blindness is in the eye. In the first way, however, only what posits something in reality can be called a being. In the first way, therefore, blindness and the like are not beings.

5. So, the word “essence” is not taken from the word “being” used in the second way; for some things which do not have an essence are called beings in this way as is clear in the case of privations. Rather, the word “essence” is taken from the word “being” used in the first way. It is for this reason that the Commentator says in the same place that the word “being” used in the first way is what signifies the essence of a real thing.

6. And because the word “being” used in this way is used apropos of what is divided into the ten genera, as we have said, the word “essence” must signify something common to all natures, by means of which (nature) diverse beings are placed into diverse genera and species; as, for example, humanity is the essence of man, and so with other things.

7. And because that by which a real thing is constituted in its proper genus or species is what is signified by the definition expressing what the real thing is, philosophers sometimes use the word “quiddity” for the word “essence.” This is what the Philosopher often calls what something was to be, i.e., that by which it belongs to something to be what it is.

8. It is also called form, in the sense in which the word “form” signifies the full determination of each real thing, as Ibn-Sînâ says in the second book of his Metaphysics.

9. Further, it is given another name, nature, taking the word “nature” in the first of the four ways given by Boethius in his book On the Two Natures. In this way, whatever can in any way be grasped by the intellect is called a nature. For a real thing is not intelligible except through its definition and essence.

10. The Philosopher, too, says in the fifth book of the Metaphysics that every substance is a nature. But the word “nature” taken in this way appears to signify the essence of a real thing according as it has an ordering to the thing’s proper operation; and no real thing lacks a proper operation.

11. The name “quiddity,” however, is taken from the fact that what is signified by the definition is the essence. But it is called essence from the fact that through it and in it a real being has existence.

12. Because the word “being” is used absolutely and with priority of substances, and only posteriorly and with qualification of accidents, essence is in substances truly and properly, in accidents only in some way with qualification.

13. Further, some substances are simple and some are composed, and essence is in each. But essence is in simple substances in a truer and more noble way, according to which they also have a more noble existence; for they ─ at least that simple substance which is first, and which is God ─ are the cause of those which are composed. But because the essences of the simple substances are more hidden from us, we ought to begin with the essences of composed substances, so that we may progress more suitably in learning from what is easier.

14. In composed substances there are form and matter, for example, in man soul and body.

15. But we cannot say that either one of them alone may be said to be the essence. That matter alone is not the essence of a real thing is clear, since through its essence a real thing is knowable and assigned to a species or to a genus. But matter alone is neither a principle of knowledge, nor is it that by which something is assigned to a genus or to a species; rather a thing is so assigned by reason of its being something actual.

16. Neither can the form alone of a composed substance be said to be its essence, although some try to assert this. For it is evident from what has been said that essence is what is signified by the definition of a real thing. And the definition of natural substances contains not only form, but matter as well; otherwise natural definitions and mathematical ones would not differ.

17. Neither can it be said that matter is placed in the definition of a natural substance as something added to its essence or as something outside its essence, because this mode of definition is proper to accidents, which do not have a perfect essence. This is why accidents must include in their definition a subject which is outside their genus. It is clear therefore that essence includes matter and form.

18. Further, neither can it be said that essence signifies some relation between matter and form or something added to them, because this would of necessity be an accident or something extraneous to the real thing, and the real thing would not be known through it. And these are traits of essence. For through the form, which is the actuality of matter, matter becomes something actual and something individual. Whence what supervenes does not confer on matter actual existence simply, but such an actual existence; as accidents in fact do. Whiteness, for example, makes something actually white. Whence the acquisition of such a form is not called generation simply, but generation in a certain respect. It remains, therefore, that the word “essence” in composed substances signifies that which is composed of matter and form.

19. Boethius is in agreement with this in his commentary on the Predicaments, where he says that ousia signifies the composite. For ousia in Greek is the same as essentia in Latin, as he himself says in his book On the Two Natures. Ibn-Sînâ, too, says that the quiddity of composed substances is the composition itself of form and matter. And the Commentator, likewise, in his considerations on the seventh book of the Metaphysics says: “The nature which species have in generable things is something in between, i.e., composed of matter and form.”

20. Reason, too, is in accord with this, because the existence of a composed substance is not the existence of the form alone nor of the matter alone, but of the composite itself; and essence is that according to which a real thing is said to be. Whence it is necessary that the essence, whereby a real thing is denominated a being, be neither the form alone nor the matter alone, but both, although the form alone in its own way is the cause of such existence.

21. We see the same in other things which are constituted of a plurality of principles, namely, that the real thing is not denominated from one of these principles alone, but from what includes both, as is evident in the case of tastes. Sweetness, for example, is caused by the action of what is hot dispersing what is moist; and although heat in this way is the cause of sweetness, a body is not denominated sweet from heat, but from the taste which includes what is hot and what is moist.

22. But matter is the principle of individuation. From this it might perhaps appear to follow that an essence which includes in itself matter along with form is only particular and not universal. And from this it would follow that universals would not have a definition, if essence is that which is signified by a definition.

23. We should notice, therefore, that the principle of individuation is not matter taken in just any way whatever, but only designated matter. And I call that matter designated which is considered under determined dimensions. Such matter is not placed in the definition of man as man, but it would be placed in the definition of Socrates, if Socrates had a definition. Rather, it is non-designated matter which. is placed in the definition of man; for this bone and this flesh are not placed in the definition of man, but bone and flesh absolutely. These latter are man’s non-designated matter.

24. It is clear, therefore, that the essence of man and the essence of Socrates do not differ, except as the non-designated from the designated. Whence the Commentator says in his considerations on the seventh book of the Metaphysics that “Socrates is nothing other than animality and rationality, which are his quiddity.”

25. The essence of the genus and that of the species also differ in this way, i.e., as the non-designated from the designated, although the mode of the designation differs in each case. Whereas the designation of the individual with respect to the species is through matter determined by dimensions, the designation of the species with respect to the genus is through the constitutive difference which is taken from the form of the thing.

26. This designation which is in the species with respect to the genus is not through something in the essence of the species which is in no way in the essence of the genus; rather, whatever is in the species is also in the genus, but as undetermined. For, if animal were not the whole that man is, but a part of man, it would not be predicated of man, since no integral part may be predicated of its whole.

27. We can see how this comes about if we examine how body taken as part of animal differs from body taken as genus; for body cannot be a genus in the same way in which body is an integral part.

28. The word “body” can be taken in many ways. Body according as it is in the genus substance is so called from the fact that it has a nature such that three dimensions can be designated in it; but the three designated dimensions themselves are a body according as body is in the genus quantity. Now, it happens in things that what has one perfection may also attain to further perfection. This is clear, for example, in man who has a sensitive nature, and further an intellectual nature. Similarly, another perfection, such as life or some other such perfection, can be added to the perfection of having a form such that three dimensions can be designated in it. The word “body,” therefore can signify some real thing which has a form from which follows the possibility of designating in it three dimensions, and signify this in an excluding way, i.e., in such a way such that no further perfection may follow from that form; in a way such that if anything be added, it is outside the signification of body. Taken in this way, body will be an integral and material part of animal because soul will be outside what is signified by the word “body”; the soul will be something over and above the body, in a way such that animal is constituted out of these two as out of parts, i.e., out of soul and body.

29. The word “body” can also be taken in another way, namely, to signify a thing which has a form such that three dimensions can be designated in it, no matter what sort of form it is, whether some further perfection can come from it or not. And taken in this way, body will be a genus of animal, because there is nothing in animal which is not implicitly contained in body. Soul is not a form other than the form through which three dimensions could be designated in that thing; thus, when we said that body is that which has a form such that because of it three dimensions can be designated in the body, form meant any form, whether animality or stoneness, or any other form. And so the form of animal is implicitly contained in the form of body, when body is its genus.

30. And such likewise is the relation of animal to man. For, if animal were to name only that thing which has a perfection such that it can sense and be moved by a principle within itself, and name this thing as excluding other perfection, then any further perfection would be related to animal as a part, and not as implicitly contained in the notion of animal; and so, animal would not be a genus. Animal is a genus according as it signifies a thing from whose form the senses and movement can come forth, no matter what sort of form it is, whether a sensible soul only or a soul which is both sensible and rational.

31. The genus, thus, signifies indeterminately everything that is in the species; it does not signify the matter alone. Similarly, the difference, too, signifies everything in the species, and not the form alone; the definition, too, signifies the whole, and so does the species, but in diverse ways.

32. The genus signifies the whole as a name determining what is material in the real thing without the determination of the proper form. Whence the genus is taken from the matter, although it is not the matter. And from this it is clear that a body is called a body from the fact that it has a perfection such that three dimensions can be designated in the body, and that this perfection is related materially to further perfection.

33. The difference, on the contrary, is a name taken from a determinate form, and taken in a determinate way, i.e. as not including a determinate matter in its meaning. This is clear, for example, when we say animated, i.e., that which has a soul; for what it is, whether a body or something other, is not expressed. Whence Ibn-Sînâ says that the genus is not understood in the difference as a part of its essence, but only as something outside its essence, as the subject also is understood in its properties. And this is why the genus is not predicated essentially of the difference, as the Philosopher says in the third book of the Metaphysics and in the fourth book of the Topics, but only in the way in which a subject is predicated of its property.

34. The definition, lastly, and the species include both, namely the determinate matter which the name of the genus designates, and the determinate form which the name of the difference designates.

35. From this it is clear why the genus, the difference, and the species are related proportionately to the matter, to the form, and to the composite in the real world, although they are not identical with them.

36. The genus is not the matter, but taken from the matter as signifying the whole; nor is the difference the form, but taken from the form as signifying the whole.

37. Whence we say that man is a rational animal, and not that man is made up of animal and rational as we say that man is made up of soul and body. Man is said to be composed of soul and body as some third thing constituted of two other things, and which is neither of them. For man is neither soul nor body. But if man may be said in some way to be composed of animal and rational, it will not be as a third thing out of two other things, but as a third concept out of two other concepts. For the concept “animal” is without the determination of the form of the species, and it expresses the nature of a thing from that which is material in relation to the ultimate perfection. But the concept of the difference “rational” consists in the determination of the form of the species. And from these two concepts the concept of the species or of the definition is constituted. And thus just as the constituents of a real thing are not predicated of that real thing, so too the concepts which are constituents of another concept are not predicated of that concept; for we do not say that the definition is the genus or the difference.

38. Although the genus signifies the whole essence of the species, it is not necessary that the diverse species in a same genus have one essence.

39. For the oneness of the genus proceeds from its very indetermination or indifference; not however in such a way that what is signified by the genus is some numerically one nature found in diverse species, and to which another thing supervenes, namely the difference, determining the genus as form determines matter which is numerically one. It is rather because the genus signifies some form, not determinately this form or that form, which the difference expresses determinately, but which is not other than the form which was indeterminately signified by the genus.

40. This is why the Commentator says in his considerations on the eleventh book of the Metaphysics that prime matter is said to be one by reason of the removal of all forms, whereas the genus is said to be one by reason of the commonness of the designated form.

41. Whence, it is clear that when one adds the difference and removes that indetermination which was the cause of the oneness of the genus, there remain species which are diverse in essence.

42. The nature of the species, as we have said, is indeterminate in relation to the individual, as the nature of the genus is indeterminate in relation to the species.

43. Because of this, just as that which is a genus, as predicated of the species, implies in its signification, though indistinctly, everything that is determinately in the species; so too that which is a species, according as it is predicated of the individual, must signify, though indistinctly, everything which is essentially in the individual.

44. And it is in this way that the essence of the species is signified by the word “man”; whence man is predicated of Socrates. But if the nature of the species is signified as excluding designated matter, which is the principle of individuation, it will be as a part; and in this way it is signified by the word “humanity,” for humanity signifies that by which man is man; and it is not the case that man is man by reason of designated matter. And so designated matter is in no way included among the things by which man is man. Since, therefore, humanity includes in its concept only those things by which man is man, it is clear that designated matter is excluded from or is cut out of its signification. And because a part is not predicated of its whole, humanity is not predicated of man, nor is it predicated of Socrates.

45. Whence Ibn-Sînâ says that the quiddity of a composite is not the composite itself whose quiddity it is, even though the quiddity too is composed. Humanity, for example, though composed, is not man; it must be received into something which is designated matter.

46. As we have said, the designation of the species with respect to the genus is through forms, whereas the designation of the individual with respect to the species is through matter. This is why the word which signifies that from which the nature of the genus is taken, and signifies it as excluding the determinate form which perfects the species, must signify a material part of the whole, as, for example, body is a material part of man. But the word which signifies that from which the nature of the species is taken, and signifies it as excluding designated matter, signifies a formal part.

47. And thus humanity is signified as a certain form, and it is said to be the form of the whole, not indeed as something added to the essential parts, namely to form and matter, as the form of a house is added to its integral parts; rather, it is a form which is a whole, that is, a form which includes both form and matter, but which excludes those things by reason of which matter can be designated.

48. It is clear, therefore, that the word “man” and the word “humanity” signify the essence of man, but diversely, as we have said; the word “man” signifies it as a whole, inasmuch as it does not exclude designation by matter, but contains it implicitly and indistinctly, as we have said before that the genus contains the difference. And this is why the word “man” is predicated of individuals. But the word “humanity” signifies it as a part, because it contains in its signification only what belongs to man as man, and it excludes all designation by matter. Whence it is not predicated of individual men.

49. And this is why the word “essence” is sometimes found predicated of a real thing, for we say that Socrates is a certain essence; and sometimes it is denied, as when we say that the essence of Socrates is not Socrates.

50. Having seen what is signified by the word “essence” in composed substances, we must see how a composed essence is related to the notion of the genus, of the species, and of the difference.

51. Because that to which the notion of the genus, or of the species, or of the difference, belongs is predicated of this designated singular, it is impossible that the notion of a universal ─ e.g., of the genus or of the species ─ belong to an essence according as it is signified a part, as by the word “humanity” or “animality.” And this is why Ibn-Sînâ says that rationality is not a difference, but the principle of a difference. And for the same reason humanity is not a species, and animality not a genus.

52. Similarly, it cannot be said that the notion of the genus, or of the species, belongs to an essence as to some real thing existing outside singular things, as the Platonists held, because in this way the genus and the species would not be predicated of this individual; for it cannot be said that Socrates is what is separated from him. Nor, further, would this separated something be of any use in knowing this singular.

53. Whence it remains that the notion of the genus, or of the species, belongs to an essence according as it is signified as a whole, as by the word “man” or “animal” according as it contains implicitly and indistinctly everything that is in the individual.

54. Now, a nature or essence signified as a whole can be considered in two ways. In one way it can be considered according to its proper content, and this is an absolute consideration of it. And in this way nothing is true of it except what belongs to it as such; whence if anything else is attributed to it, the attribution is false. For example, to man as man belong rational and animal, and whatever else falls in his definition. But white or black, or anything of this sort, which is not of the content of humanity, does not belong to man as man. Whence, if one should ask whether the nature so considered can be said to be one or many, neither should be allowed, because each is outside the content of humanity and either can be added to it. For if plurality were of its content, it could never be one, as it is in Socrates. Similarly, if oneness were of its content, then the nature of Socrates and Plato would be one and the same, and it could not be plurified into many individuals.

55. In the other way an essence is considered according to the existence it has in this or that. When the essence is so considered, something is predicated of it accidentally, by reason of that in which it is; for example, it is said that man is white because Socrates is white, although to be white does not belong to man as man.

56. This nature has a twofold existence, one in singular things, the other in the soul; and accidents follow upon the nature according to either existence. In singular things it has a multiple existence in accord with the diversity of these singular things; yet the existence of none of these things belongs to the nature considered in itself, i.e., absolutely. For it is false to say that the nature of man, as such, has existence in this singular thing; because if existence in this singular thing belonged to man as man, man would never exist outside this singular thing. Similarly, if it belonged to man as man not to exist in this singular thing, man would never exist in it. But it is true to say that it does not belong to man as man to exist in this or that singular thing, or in the soul. It is clear, therefore, that the nature of man, absolutely considered, abstracts from any of these existences, but in a way such that it excludes no one of them.

57. And it is the nature so considered which is predicated of all individuals. Yet it cannot be said that the notion of a universal belongs to the nature so considered, because oneness and commonness are of the notion of a universal. Neither of these belongs to human nature considered absolutely, for if commonness were of the content of man, commonness would be found in whatever thing humanity is found. And this is false, because in Socrates there is no commonness, but whatever is in him is individuated.

58. Similarly, it cannot be said that the notion of the genus or of the species attaches to human nature according as it has existence in individuals, because human nature is not found in individuals with a oneness such that it would be some one thing belonging to all, which the notion of a universal requires.

59. It remains, therefore, that the notion of the species attaches to human nature according to the existence it has in the intellect.

60. For human nature exists in the intellect in abstraction from all that individuates; and this is why it has a content which is the same in relation to all individual men outside the soul; it is equally the likeness of all of them, and leads to a knowledge of all insofar as they are men. And it is from the fact that the nature has such a relation to all individuals that the intellect discovers and attributes the notion of the species to it. Whence the Commentator says in his considerations on the first book of On the Soul that “it is the intellect which causes universality in things.” Ibn-Sînâ, too, says this in his Metaphysics.

61. And although the intellectually grasped nature has the character of a universal according as it is compared to things outside the soul, because it is one likeness of all of them; still according as it exists in this intellect or in that one, it is something particular ─ a particular species grasped by a particular intellect. From this one can see the weakness of what the Commentator says in his considerations of the third book of On the Soul; from the universality of the intellectually grasped form he wanted to conclude that there is one intellect in all men. This falls short of the truth because the intellectually grasped form has its universality not according to the existence which it has in an intellect, but according as it is related to real things as a likeness of them.

62. What is true here is like what would be true of a corporeal statue representing many men: the image or form of the statue would have its own and individual existence according as it exists in this matter, and it would have the character of commonness according as it is the common representation of many.

63. Further, because it belongs to human nature absolutely considered to be predicated of Socrates, and because the notion of the species does not belong to it absolutely considered but is among the accidents which follow upon it according to the existence it has in the intellect, one can see why the word “species” is not predicated of Socrates, i.e., why it is not said that “Socrates is a species.” This would of necessity be said if the notion of the species belonged to man according to the existence which man has in Socrates; or, if the notion of the species belonged to man absolutely considered, i.e., to man as man, for whatever belongs to man as man is predicated of Socrates.

64. Still, to be predicated belongs to the genus in virtue of what it is, since this is placed in its definition. For predication is something which is achieved by the combining and dividing activity of the intellect, and which has for its foundation in the real thing the union of those things, one of which is said of another. Whence the notion of predicability can be included in the notion of that intention which is the genus, which (intention) is similarly achieved by the activity of the intellect. Nonetheless, that to which the intellect, combining one thing with another, attributes the intention of predicability is not the intention of the genus itself; rather it is that to which the intellect attributes the intention of the genus, for example, that which is signified by the word “animal.”

65. It is clear, therefore, how an essence or nature is related to the notion of the species. The notion of the species is not among the things which belong to the nature absolutely considered, nor is it among the accidents which follow upon the nature according to the existence it has outside the soul, as whiteness or blackness. Rather the notion of the species is among the accidents which follow upon the nature according to the existence it has in the intellect; and it is in this way, too, that the notion of the genus and of the difference belong to it.

66. It remains, now, for us to see in what way essence is in separated substances, namely, in the soul, in the intelligences, and in the First Cause.

67. Although everyone admits the simplicity of the First Cause, some try to introduce a composition of matter and form in the intelligences and in souls. The originator of this position appears to have been Ibn-Gabirol, author of the book Fountain of Life.

68. But this is not in agreement with what philosophers commonly say, because they call them substances separated from matter, and prove them to be without all matter. The strongest demonstration of this is from the power of understanding which is in them. For we see that forms are not actually intelligible except according as they are separated from matter and from its conditions; nor are they made actually intelligible except by the power of a substance understanding them, according as they are received into, and are affected by, that substance.

69. Whence it is necessary that there be in any intelligent substance a total freedom from matter, such that the substance does not have matter as a part of itself, such too that the substance is not a form impressed on matter, as is the case with material forms.

70. Nor can it be said that it is only corporeal matter that impedes intelligibility, and not any matter whatsoever. For if this were so by reason of corporeal matter alone, then it would have to be that matter impedes intelligibility by reason of the corporeal form, since matter is called corporeal only according as it is found under the corporeal form. But this cannot be ─ namely, that matter impedes intelligibility by reason of the corporeal form ─ because the corporeal form itself, just as other forms, is actually intelligible according as it is abstracted from matter. Whence there is in no way a composition of matter and form in the soul or in an intelligence if matter in them is taken in the sense in which matter is taken in corporeal substances.

71. But there is in them a composition of form and existence. Whence it is said, in the commentary on the ninth proposition of the Book on Causes, that “an intelligence is something having form and existence,” and form is taken there for the simple quiddity or nature itself.

72. It is easy to see how this may be so. Whatever things are so related to one another that one is a cause of the other’s existence, the one which is the cause can have existence without the other, but not conversely. Now the relation of matter and form is such that form gives existence to matter. It is impossible, therefore, that matter exist without some form. But it is not impossible that some form exist without matter, for form, to the extent that it is form, does not depend on matter. But if some forms are found which cannot exist except in matter, this happens to them because of their distance from the first principle, which is first and pure act. Whence those forms which are nearest to the first principle are forms subsisting of themselves, that is without matter. For not every sort of form needs matter, as has been said; and the intelligences are forms of this sort. And therefore it is not necessary that the essences or quiddities of these substances be other than form itself.

73. Thus the essence of a composed substance and that of a simple substance differ in this: the essence of a composed substance is not form alone, but includes form and matter; the essence of a simple substance is form alone.

74. And from this follow two other differences. One difference is that the essence of a composed substance can be signified as a whole or as a part. This happens on account of the designation of matter, as has been said. And therefore the essence of a composed thing is not predicated of the composed thing itself in just any way, for it cannot be said that man is his quiddity. But the essence of a simple thing, which (essence) is its form, cannot be signified except as a whole, since nothing is there besides the form as receiving the form. Thus, no matter what way the essence of a simple substance is taken, it is predicated of the simple substance. Whence Ibn-Sînâ says that the quiddity of a simple thing is the simple thing itself, because there is nothing other receiving the quiddity.

75; The second difference is that the essences of composed things, because they are received into designated matter, are multiplied according to its division. And this is why it happens that certain things are the same in species and diverse in number. But since the essence of a simple thing is not received into matter, such a multiplication is impossible here. And this is why, of necessity, many individuals of a same species are not found among these substances; rather, as Ibn-Sînâ expressly says, there are among them as many species as there are individuals.

76. Although substances of this sort are forms alone without matter, they are not utterly simple so as to be pure act. They have an admixture of potency, which becomes clear in the following consideration.

77. Whatever is not of the understood content of an essence or quality is something which comes from without and makes a composition with the essence, because no essence can be understood without the things which are parts of it. Now, every essence or quiddity can be understood without anything being understood about its existence. For I can understand what a man is, or what a phoenix is, and yet not know whether they have existence in the real world. It is clear, therefore, that existence is other than essence or quiddity, unless perhaps there exists a thing whose quiddity is its existence.

78. And there can be but one such thing, the First Thing, because it is impossible to plurify a thing except: (1) by the addition of some difference, as the nature of the genus is multiplied in its species, or (2) by the reception of a form into diverse matters, as the nature of the species is multiplied in diverse individuals, or (3) by this: that one is absolute and the other is received into something; for example, if there were a separated heat, it would by virtue of its very separation be other than heat which is not separated. Now, if we posit a thing which is existence alone, such that this existence is subsistent, this existence will not receive the addition of a difference because it would no longer be existence alone, but existence plus some form. And much less will it receive the addition of matter because it would no longer be a subsistent existence, but a material existence. Whence it remains that such a thing, which is its own existence, cannot be but one.

79. Whence it is necessary, that in every thing other than this one its existence be other than its quiddity, or its nature, or its form. Whence it is necessary that existence in the intelligences be something besides the form, and this is why it was said that an intelligence is form and existence.

80. Now, whatever belongs to a thing is either caused by the principles of its nature, as the ability to laugh in man, or comes to it from some extrinsic principle, as light in the air from the influence of the sun. But it cannot be that the existence of a thing is caused by the form or quiddity of that thing ─ I say caused as by an efficient cause ─ because then something would be its own cause, and would bring itself into existence, which is impossible. It is therefore necessary that every such thing, the existence of which is other than its nature, have its existence from some other thing. And because every thing which exists by virtue of another is led back, as to its first cause, to that which exists by virtue of itself, it is necessary that there be some thing which is the cause of the existence of all things because it is existence alone. Otherwise, there would be an infinite regress among causes, since every thing which is not existence alone has a cause of its existence, as has been said. It is clear, therefore, that an intelligence is form and existence, and that it has existence from the First Being, which is existence alone. And this is the First Cause, which is God.

81. Now everything which receives something from another is in potency with respect to what it receives, and what is received into it is its act. It is necessary therefore that the quiddity itself or the form, which is the intelligence, be in potency with respect to the existence which it receives from God; and this existence is received as an act. It is in this way that potency and act are found in the intelligences, but not form and matter, unless equivocally.

82. Whence, to suffer, and to receive, and to be a subject, and all things of this sort, which are observed to belong to things by reason of matter, also belong equivocally to intellectual and to corporeal substances, as the Commentator says in his considerations on the third book of On The Soul.

83. And because the quiddity of an intelligence is, as has been said, the intelligence itself, its quiddity or essence is identically that which it itself is; and its existence received from God is that whereby it subsists in reality. And this is why substances of this sort are said by some to be composed of “that by which it is” and “that which is,” or as Boethius says, of “that which is” and “existence.”

84. And because there is potency in the intelligences as well as act, it will not be difficult to find a multitude of intelligences, which would be impossible if there were no potency in them. Whence the Commentator says, in his considerations on the third book of On The Soul, that if the nature of the possible intellect were not known, we would not be able to find multitude among the separated substances. The separated substances, therefore, are distinct from one another according to their grade of potency and act, in such a way that a superior intelligence which is nearer to the First Being has more act and less potency, and so with the others.

85. This grading has its termination in the human soul, which holds the lowest grade among intellectual substances. Whence its possible intellect is related to intelligible forms in the way in which prime matter, which holds the lowest grade in sensible existence, is related to sensible forms, as the Commentator remarks in his considerations on the third book of On The Soul. And this is why the Philosopher compares it to a blank tablet on which nothing has been written.

86. And because it has more potency than other intelligible substances, the human soul is so close to material things that a material thing is drawn to it to share its existence, but in such a way that from soul and body results one existence in one composed thing; and yet this existence is not dependent on the body inasmuch as it is the soul’s existence.

87. And posterior to this form which is the soul are found other forms which have more potency, and which are still closer to matter, so close that they do not exist without matter. Among these forms, too, is found an order and a grading, down to the first forms of the elements, which are the closest to matter. These last are so close to matter that they operate only according to the active and passive qualities, and the other sorts of things, which are required as the means by which matter is disposed for the receiving of form.

88. From the preceding it is clear how essence is found in diverse substances. For we find that they have essence in three different ways.

89. There is a thing, God, whose essence is his existence itself. And this is why we find some philosophers who say that God does not have a quiddity or essence, because his essence is not other than his existence. And from this it follows that he is not in a genus, because everything which is in a genus must have a quiddity which is other than its existence. And this is so since the quiddity or nature of a genus or species, in the case of those things which have a genus or species, is not multiplied according to the intelligible content of the nature; rather, it is the existence in these diverse things which is diverse.

90. Nor is it necessary, if we say that God is existence alone, for us to fall into the error of those who say that God is universal existence whereby each and every thing formally exists. For the existence which God is, is such that no addition can be made to it. Whence by virtue of its purity it is an existence distinct from every existence. This is why, in the commentary on the ninth proposition of the Book on Causes, it is said that the individuation of the First Cause, which is existence alone, is through its pure goodness. But as regards that universal existence, just as it does not include in its intelligible content any addition, so too neither does it include in its intelligible content any exclusion of addition, because if this were the case, nothing in which something is added over and above its existence could be understood to be.

91. Similarly, although God is existence alone, it is not necessary that the other perfections or excellences be wanting in him. Rather he has all the perfections which are in every genus. This is why he is called simply perfect, as the Philosopher and the Commentator say in book five of the Metaphysics. But he has these perfections in a more excellent way than all things because in him they are one, whereas in other things they have diversity. And this is so because all these perfections belong to him according to his simple existence. If some one could perform the operations of all the qualities through some one quality, he would have every quality in that one quality; so too God has all these perfections in his existence itself.

92. Essence is found in a second way in created intellectual substances. Existence in them is other than their essence, although essence is without matter. Whence their existence is not absolute, but received, and therefore limited and confined to the capacity of the recipient nature. But their nature or quiddity is absolute, not received in any matter. And this is why it is said in the Book on Causes that the intelligences are unlimited from below and limited from above, for they are limited as regards their existence, which they receive from above; but they are not limited from below because their forms are not limited to the capacity of a matter receiving them.

93. And this is why, as has been said, there is not found among such substances a multitude of individuals in one species, with the exception of the human soul on account of the body to which it is united. And although its individuation depends on the body as upon the occasion for its beginning because it does not acquire its individuated existence except in the body of which it is the actuality, it is not necessary that its individuation be lost when the body is taken away because that existence, since it is absolute, always remains individuated once the soul acquires it by being made the form of this individual body. And this is why Ibn-Sînâ says that the individuation and multiplication of souls depends on the body as regards its beginning, but not as regards its termination.

94. And because quiddity in these substances is not the same as existence, they are orderable within a predicament. And this is why they have a genus, a species, and a difference, although their proper differences are hidden from us. For even in the case of sensible things, the essential differences themselves are not known; whence they are signified through accidental differences which rise out of the essential ones, as a cause is signified through its effect; this is what is done when biped, for example, is given as the difference of man. But the proper accidents of immaterial substances are unknown to us; whence their differences cannot be signified by us either through themselves or through accidental differences.

95. But we must notice that the genus and the difference of these substances are not taken in the same way in which the genus and the difference of sensible substances are taken. In the case of sensible substances the genus is taken from that which is material in the thing, whereas the difference is taken from that which is formal in it. Whence Ibn-Sînâ says at the beginning of his book On the Soul that form in things composed of matter and form is the simple difference of that which is constituted by it; but not in such a way that the form is the difference, but because the form is the principle of the difference, as the same writer says in his Metaphysics. And this sort of difference is called a simple difference because it is taken from what is part of the quiddity of the thing, namely, from the form. But since immaterial substances are simple quiddities, their difference cannot be taken from what is part of the quiddity, but from the whole quiddity. This is why Ibn-Sînâ says, at the beginning of On the Soul, that only those species have a simple difference whose essences are composed of matter and form.

96. Similarly, their genus too is taken from the whole essence, but in a different way, for separated substances agree with each other in immateriality, and differ from each other in grade of perfection, according as they withdraw from potentiality and approach pure actuality. The genus is taken from that in them which follows upon their being immaterial; for example, intellectuality or something of this sort. But the difference, which is unknown to us, is taken from that in them which follows upon their grade of perfection.

97. And it is not necessary that these differences be accidental because they are determined by greater and lesser perfection which does not diversify a species. For grades of perfection in the reception of a same form do not diversify a species, as whiter and less white in participating whiteness which is of the same nature. But a diverse grade in the forms or natures themselves which are participated does diversify a species. For example, nature proceeds by grades from plants to animals by way of certain things which are midway between animals and plants, according to the Philosopher in book seven of On Animals. Nor, similarly, is it necessary that intellectual substances be divided always by two true differences, because this cannot come about in the case of all things, as the Philosopher says in book eleven of On Animals.

98. Essence is found in a third way in substances composed of matter and form. Here it is both the case that existence is received and limited because they have existence from another; and that their nature or quiddity is received in designated matter. And so, they are limited both from above and from below. And because of the division of designated matter, the multiplication of individuals in one species is here possible. As regards the question how the essence of these substances is related to the logical intentions, we have explained that above.

99. What remains now is to see how essence is in accidents; how it is in all substances has been discussed.

100. And because essence, as has been said, is that which is signified by the definition, it is necessary that accidents have essence in the way in which they have definition. They have an incomplete definition because they cannot be defined unless a subject is placed in their definition. And this is so because they do not have existence in themselves free of a subject.

101. But just as a substantial existence results from matter and form when they are composed, so from an accident and a subject results an accidental existence when the accident comes to the subject. And this is also why neither substantial form nor matter have a complete essence because it is necessary to place in the definition of substantial form that of which it is the form; and so its definition is formulated by the addition of something which is outside its genus, just like the definition of an accidental form. Whence, also, the body is placed in the definition of the soul by the natural philosopher, who considers the soul only insofar as it is the form of a physical body.

102. But there is this difference between substantial and accidental forms. Just as substantial form does not have existence in itself, separately from that to which it comes, neither does that to which it comes, namely, matter. And thus from the conjunction of the two results that existence in which a thing subsists in itself, and from them is produced something essentially one; and because of this an essence is the result of their conjunction. Whence, although the form considered in itself does not have the complete nature of an essence, it is nonetheless part of a complete essence. But that to which an accident comes is a being complete in itself and subsisting in its own existence. And this existence naturally precedes the accident which supervenes. And this is why the supervening accident does not, by its conjunction with that to which it comes, cause that existence in which a thing subsists, and through which the thing is a being in itself. It causes, rather, a certain second existence, without which the subsisting thing can be understood to be, just as what is first can be understood without what is second. Whence something essentially one is not produced from an accident and a subject, but something accidentally one. And this is why an essence does not result from their conjunction, as from the conjunction of form and matter. And this is why an accident neither has the nature of a complete essence, nor is it part of a complete essence. But just as it is a being in a qualified way, so too does it have essence in a qualified way.

103. Now, whatever is said to be most fully and most truly in any genus is the cause of the things which are posterior in that genus; for example, fire, which is unsurpassed in heat, is the cause of heat in hot things, as it is said in the second book of the Metaphysics. This is why substance, which has first place in the genus of being, having essence most truly and most fully, must be the cause of accidents, which participate in the nature of being secondarily and in a qualified way.

104. But this happens in diverse ways. For, since the parts of substance are matter and form, certain accidents follow principally on form, certain others follow principally on matter. There are forms whose existence does not depend on matter, for example, intellectual souls; but matter does not have existence except through form. Whence some of the accidents which follow on form are such that they share nothing with matter; for example, to understand, which does not take place through a bodily organ, as the Philosopher proves in the third book of On the Soul. But some other of the accidents following on form are such that they do share something with matter; for example, to sense. But no accident follows on matter which shares nothing with form.

105. Among those accidents which follow on matter we find a certain diversity. For some accidents follow on matter according to the ordering which it has to a special form; for example, male and female among animals, the diversity of which derives from matter, as is said in the tenth book of the Metaphysics. Whence these accidents do not remain on the removal of the form of animal, except equivocally. Other accidents follow on matter according to the ordering which lt has to a general form. Thus, on the removal of the special form they still remain in the matter; for example, the blackness of an Ethiopian’s skin is from the mixture of the elements and not from his soul; and this is why it remains in him after death. And because each and every thing is individuated by matter and placed in a genus or species by its form, accidents which follow on matter are accidents of the individual, and it is according to these that individuals of a same species differ from one another.

106. But accidents following on form are the proper attributes of the genus or of the species. Whence they are found in every thing which participates in the nature of the genus or of the species. For example, man’s ability to laugh follows on the form because laughter takes place by reason of the fact that a man’s soul has grasped something.

107. It should also be noticed that sometimes the essential principles cause accidents in a state of perfect actuality, as heat in the case of fire which is always actually hot. But sometimes they cause accidents which are only aptitudes, their completion being received from an exterior agent; for example, transparency in the air, which is completed by some exterior light-emitting body. And in such things the aptitude is an inseparable accident, but the completion, which comes from some principle which is outside the essence of the thing, or which does not enter the constitution of the thing, is separable; for example, being moved and things of this sort.

108. It should be noticed, further, that the genus, the species, and the difference of accidents are taken in a way which differs from the way in which those of substances are taken.

109. In substances something essentially one results from the substantial form and matter, a certain nature results from their conjunction, a nature which is properly placed in the predicament of substance. This is why concrete names of substances which signify the composite are properly said to be in a genus, as species or genera; for example, man or animal. But the form, or the matter, is not in a predicament in this way, though each is in a predicament by reduction, as principles are said to be in a genus. Something essentially one does not, on the contrary, result from an accident and its subject. Whence the result of their conjunction is not a certain nature, to which the intention of genus or species may be attributed. Whence names of accidents expressed concretely are not placed in a predicament as species or genera; for example, white or musical, except by reduction. They are placed in a predicament only according as they are signified in the abstract; for example, whiteness and music.

110. And because accidents are not composed of matter and form, their genus cannot be taken from matter and their difference from form, as in the case of composed substances. Rather, their first genus must be taken from their way of existing itself, according to which the word “being” is diversely predicated of the ten genera according to a priority and posteriority; for example, an accident is called quantity from the fact that it is the measure of substance, and quality according as it is the disposition of substance, and so with the other accidents, according to the Philosopher in the fourth book of the Metaphysics. But their differences are taken from the diversity of the principles by which they are caused. And because proper attributes are caused by the proper principles of the subject, the subject is placed in their definition to function as the difference if they are defined in the abstract, which is the way in which they are properly in a genus; as when it is said that snubnosedness is the turned-up-ness of the nose. But the converse would be the case if their definition were taken according as they are said concretely. For in this way the subject is placed in their definition as a genus because they are then being defined after the manner of composed substance, in which the genus is taken from matter; as when we say that a snub nose is a turned up nose.

111. We have a similar case if one accident is the principle of another, as action and passion and quantity are principles of relation. And this is why the Philosopher divides relation according to these in book five of the Metaphysics.

112. But because the proper principles of accidents are not always manifest, we sometimes take the difference of accidents from their effects; as when concentrating and diffusing are called the differences of color. These effects are caused by the abundance and the scarcity of light, which cause the diverse species of color.

113. And so it is clear how essence is in substances and in accidents, and how it is in composed substances in simple ones, and how the universal intentions of logic are found in all of these, with the exception of the First Principle, which is infinitely simple, and to which, because of its simplicity, belongs the notion neither of the genus nor of the species, nor consequently definition. With this, let the discussion, its tasks achieve brought to a close.