Commentary on Aristotle's Metaphysics

 PROLOGUE

 BOOK I

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 LESSON 13

 LESSON 14

 LESSON 15

 LESSON 16

 LESSON 17

 BOOK II

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 BOOK III

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 LESSON 13

 LESSON 14

 LESSON 15

 BOOK IV

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 LESSON 13

 LESSON 14

 LESSON 15

 LESSON 16

 LESSON 17

 BOOK V

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 LESSON 13

 LESSON 14

 LESSON 15

 LESSON 16

 LESSON 17

 LESSON 18

 LESSON 19

 LESSON 20

 LESSON 21

 LESSON 22

 BOOK VI

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 LESSON 13

 LESSON 14

 LESSON 15

 LESSON 16

 LESSON 17

 BOOK VIII

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 BOOK X

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 Book XI

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 LESSON 13

 BOOK XII

 LESSON 1

 LESSON 2

 LESSON 3

 LESSON 4

 LESSON 5

 LESSON 6

 LESSON 7

 LESSON 8

 LESSON 9

 LESSON 10

 LESSON 11

 LESSON 12

 Footnotes

LESSON 11

What Forms Are Parts of the Species and of the Intelligible Expression

  Chapter II: 1036a 26-1037b 7

             629. Now the problem rightly arises as to what parts are parts of the species, and which are not parts of the species but of the concrete whole. For if this is not clear it is impossible to define anything, because definition refers to the universal and the species. Hence, if it is not evident as to what parts are material and what are not, the intelligible expression of the thing will not be clearly known.

             630. Therefore in the case of all those things which seem to be produced in specifically different matters, as a circle in bronze and in stone and in wood, it seems to be evident that none of these, either bronze or stone or wood, belong to the substance of a circle, because it can be separated from them. And with regard to those things which do not seem to be separable, nothing prevents them from being similar to these, as, for instance, if all sensible circles were of bronze; for none the less the bronze would be no part of the species. But it is difficult to separate it in the mind; for example, the species of man always appears in flesh and bones and such parts. Hence the question arises whether these are parts of the species and intelligible expression of man, or are not but have the character of matter. But since such species do not occur in other matters, we cannot separate them.

             631. Now since this seems to be possible, but it is not clear when, some thinkers are puzzled even in the case of a circle and a triangle, as if it were not right to define these by lines and by what is continuous, but that all these should be predicated in a way similar to the flesh and bones of a man and the bronze and stone of a circle. And they refer all things to numbers and say that the intelligible expression of a line is that of the number two. And of those who speak of Ideas, some claim that the number two is the line itself, and others claim that it is the Form of a line; for some say that a Form and the thing of which it is the Form are the same, for example, the number two and the Form of twoness; but this is not so in the case of a line.

             632. It follows, then, that there is one Form of many things whose Form appears to be different; and this is a conclusion that also faced the Pythagoreans (68).

             633. And it is possible [according to this view] to make one Form proper to all things, and to maintain that nothing else is a Form at all.

             634. However, in this way all things will be one. Therefore that the questions about definitions constitute a problem, and why, has been stated.

             635. Hence to reduce all things in this way and to do away with matter is superfluous; for perhaps some things are a this in this, or are things having these two principles. And the analogy of the animal, which the younger Socrates was accustomed to state, is not a good one; for it leads us away from the truth and makes us suppose that it is possible for man to exist without parts, as a circle exists without bronze. But this case is not similar; for an animal is something sensible and cannot be defined without motion, and therefore it cannot be defined without its parts being disposed in some way. For it is not a hand in any condition which is part of a man, but when it is capable of performing the function of a hand. Hence it is a part when it is animated, but it is not a part when it is not animated.

             636. And with regard to the objects of mathematics the question arises why the intelligible structures of the parts are not parts of the intelligible structure of the whole (for example, why semicircles are not parts of the intelligible structure of a circle), for they are not sensible. But perhaps this makes no difference; for there will be matter of certain things and of those which are not sensible. And this will be true of everything which is not an essence or species considered in itself, but a particular thing. Therefore the semicircle will not be part of the circle which is universal, but semicircles will be parts of singular circles, as was said before (627); for some matter is sensible and some intelligible.

             637. And it is also evident that the soul is a primary substance, and that the body is matter, and that man or animal is the composite of both taken universally. And Socrates and Coriscus are composed of soul and body taken individually, i.e., if the term soul is taken in two senses; for some take soul as soul and others as the whole. But if soul and body without qualification mean this individual soul and this individual body, each term is used both as a universal and as a singular.

             638. But whether there are besides the matter of such substances other substances as well, and whether it is necessary to look for some different substance in these, such as numbers or something of this kind, must be examined later (Books XIII & XIV); for it is for the sake of these too that we are trying to define sensible substances, since in a sense the study of sensible substances constitutes the work of the philosophy of nature, or second philosophy. For the philosopher of nature must have scientific knowledge not only of matter but of the part which is intelligible, and the latter is the more important. And with regard to definitions the philosopher must know how the parts in the intelligible expression are disposed, and why the definition is one intelligible expression; for it is evident that a thing is one. But how a thing having parts is one must be examined later (733).

             639. We have stated, then, what the essence of a thing is and how it is predicated essentially of all things (582), as well as why the intelligible expression of the essence of some things contains the parts of the thing defined, and why that of others does not. And we have also stated that those parts which have the nature of matter are not found in the intelligible expression of substance; for they are not parts of that substance, but of the whole. And in one sense there is an intelligible expression of this and in another sense there is not; for there is no intelligible expression that involves matter, because this is indeterminate. But there is an intelligible expression of the whole with reference to primary substance; for example, in the case of man there is an intelligible expression of the soul; for the substance of a thing is the specifying principle intrinsic to it, and the whole substance is composed of this along with matter. Concavity, for example, is such a principle, for from this and from nose snubnose and snubness are derived. For nose is also contained twice in these expressions; but in the whole substance or in snubnose or in Callias matter is also present. And we have also stated that in some cases the essence of the thing is the same as the thing itself, as in the case of primary substances; for curvature and the essence of curvature are the same, if curvature is primary. And by primary I mean what does not refer to something as existing in something else as its subject or matter. But all things which have the nature of matter or are conceived with matter, are not the same--not even if they are one accidentally, as Socrates and musician, for they are accidentally the same (590).

COMMENTARY

             1501. In this part he solves a problem which could arise from the answer to the foregoing question; for in answering that question he had distinguished the parts of the species from those of the individual thing, which is composed of species and matter. Hence he now inquires as to what parts are parts of the species and what are not.

             This part is therefore divided into three sections. In the first (629:C 1501) he solves the problem. In the second (638:C 1525) he shows what remains to be discussed ("But whether"). In the third (639:C 1529) he summarizes the points discussed ("We have stated").

             He accordingly says, first (629), that since it has been stated that the parts of the species are given in definitions, but not the parts of the thing composed of matter and species, there is a real problem as to what parts are parts of the species, and what are not parts of the species "but of the concrete whole," i.e., the individual thing, in which the nature of the species is taken along with individuating matter.

             1502. For if this is not evident, we will be unable to define anything correctly, because definition never pertains to the singular but only to the universal, as was stated above (627:C 149397). And among universals the species is properly included, and this is constituted of genus and difference, of which every definition is composed; for a genus is defined only if there is also a species. Hence it is clear that unless we know what part has the nature of matter, and what part does not but pertains to the species itself, it will not be evident as to what definition should be assigned to a thing, since it is assigned only to the species. And in the definition of the species it is necessary to give the parts of the species and not those which are subsequent to it.

             1503. Therefore in the case (630).

             He solves the proposed problem; and in regard to this he does three things. First (630:C 1503), he gives the solution according to the opinion of the Platonists. Second (632:C 1512), he rejects it ("It follows"). Third (635:C 1516), he solves it by giving his own opinion ("Hence to reduce").

             In regard to the first he does two things. First, he solves the proposed difficulty in reference to sensible things; and second (631:C 1507), in reference to the objects of mathematics ("Now since this seems").

             He says, first (630), then, that in the case of some things it is evident that matter is not part of the species, for example, all those which appear to be produced in specifically different matters, as a circle is found to be produced in bronze, in stone and in wood. Hence it is evident that neither bronze nor stone nor wood is part of the substance of circle, as though it were a part of the form, circle. And this is evident by reason of the fact that circle may be separated from each of these matters, and nothing can be separated from something which is a part of its form.

             1504. But there are some things whose species do not occur as produced in specifically different matters, but always in the same matters; for example, the species of man insofar as it is apparent to the sense of sight is found only in flesh and bones. However, nothing prevents those things which do not seem to be separate from their proper matter from also being related in the same way to their own matters as those things which can exist in different matters and be separated from each of them.

             1505. For if we were to maintain that some circles would not be apparent to the senses unless they were composed of bronze, none the less bronze would not be in this way a part of the form of circle. And even though circle would not then be actually separate from bronze, it would still be separable in thought, since the species of circle can be understood without bronze, since bronze is not part of the form of circle, although it is difficult to mentally separate and isolate from each other those things which are not actually separate; for this belongs only to those things which can be raised above the sensible order by the intellect.

             1506. And similarly, if the species of man always appears in flesh and bones and such parts, it is necessary to ask whether these are parts of man's species "and of the intelligible expression," or definition, of man; or whether they are not the species' parts, but only the matter of the species, as bronze is the matter of a circle. But because such a species does not arise in other material parts than these, therefore we cannot by means of our intellect easily separate man from flesh and bones; for the reasoning seems to be the same in this case as in that of a circle, if all circles were of bronze.

             1507. Now since this (631).

             Then he continues his discussion by examining the opinion just touched on insofar as it relates to the objects of mathematics. He says that in some cases it seems possible for matter not to be a part of the species, although the species occurs only in matter, but it is not evident when and in what instances this is possible or not possible. Therefore some thinkers are puzzled about this, not only in reference to natural things but also in reference to the objects of mathematics, such as circles and triangles.

             1508. For it seems to them that, just as sensible matter is not a part of the species of natural beings, in a similar fashion intelligible matter is not a part of the species of mathematical entities. Now the intelligible matter of mathematical figures is continuous quantity, such as lines and surfaces. Hence it was thought that a line is not part of the species of a circle or triangle (as if it were not right that a triangle and a circle should be defined by lines and by continuous quantity, since they are not parts of the species), but that all those things are related to a circle and a triangle in the same way that flesh and bones are related to man, and bronze and stones to circles.

             1509. But when the continuous quantity, line, is removed from triangles and circles, the only thing that remains is the unit and number, because a triangle is a figure having three lines, and a circle is a figure having one. Therefore, not holding that lines are parts of the species, they refer all species to numbers, saying that numbers are the species of all mathematical entities; for they say that the intelligible structure of the number two is that of a straight line, because a straight line is terminated by two points.

             1510. But among the Platonists, who posit Ideas, there is a difference of opinion on this matter; for some of them, i.e., those who did not make the objects of mathematics an intermediate class between the Forms and sensible things but claimed that the Forms are numbers, said that the line is the number two, because they did not hold that there is an intermediate line differing from the Form of a line.

             1511. But others said that the number two is not a line but the Form of a line; for according to them the line is a mathematical intermediate between the Forms and sensible things; and they said that the number two is the Form itself of the number two. And according to them there are some things in which the Form and the thing of which it is the Form do not differ, for example, numbers. Hence they said that the number two and the Form of twoness are the same. But this is not the case with a line, in their opinion, because a line already expresses something participating in a Form, since there are found to be many lines in one species; and this would not be so if the line itself were a separate Form.

             1512. It follows, then (632).

             He now rejects the solution given above; and he gives three arguments, of which the first is this: if numbers alone are separate Forms, all things which participate in one number will participate in one Form. But there are many specifically different things which participate in one number; for one and the same number is present in a triangle because of its three lines, and in a syllogism because of its three terms, and in a solid because of its three dimensions. Hence it follows that there is one Form of many things which are specifically different. This was the conclusion which faced not only the Platonists but also the Pythagoreans, who also claimed that the nature of everything consists in numbers.

             1513. And it is possible (633).

             Then he gives the second argument, which is as follows: if flesh and bones are not parts of the Form of man, and lines not parts of the Form of triangle, then for a like reason no matter is part of a Form. But in the case of numbers, according to the Platonists, the number two is attributed to matter and unity to Form. Therefore only unity constitutes Form. But the number two, and therefore all other numbers, inasmuch as they imply matter, will not be Forms. Hence there will only be one Form of all things.

             1514. However, in this way (634).

             Here he gives the third argument, which is as follows: those things are one whose Form is one. Hence if there is only one Form of all things, it follows that all things are one formally, and not just those which seem to be different [but in reality are not]. Yet it can be said that this third argument does not differ from the second one, but that it is an absurdity which follows as a conclusion of the second argument.

             1515. Therefore having given the arguments on which the foregoing solution is based, and having given two arguments against this solution, he concludes that the questions about definitions constitute a problem, and that the reason for this has been stated. Thus it is evident that he wishes to use everything which has been set down to expose the difficulty connected with the foregoing problem.

             1516. Hence to reduce (635).

             He now gives the real solution of the foregoing problem based on his own doctrine. He does this first with regard to natural things; and second (636:C 1520), with regard to the objects of mathematics ("And with regard").

             He accordingly says, first (635), that since the absurdities mentioned above plague those removing from the species of a thing all material parts, whether they are sensible or not, it is evident from what has been said that it is futile to reduce all species of things to numbers or to the unit and to do away completely with sensible and intelligible matter as the Platonists did.

             1517. For some forms of things are not forms without matter, but are "a this in this," i.e., a form in matter, in such a way that what results from the form existing in matter is the species. Or if they are not like a form in matter, they are like things which have a form in matter; for properly speaking natural things have form in matter, and the objects of mathematics also resemble these in a way inasmuch as the figure of a circle or a triangle is related to lines as the form of man is related to flesh and bones. Therefore just as man's species is not a form without flesh and bones, neither is the form of a triangle or of a circle a form without lines. Hence the analogy of animal, which the younger Socrates was accustomed to use, is not a good one.

             1518. Now it seems that Plato himself is called the younger Socrates, because in all his works he introduces Socrates as the speaker, since Socrates was his master. And Plato's opinion about the materiality of natural species he calls an analogy, because it is similar to fables, which are devised for the purpose of conveying some opinion by means of a metaphor; and this is why he said above in Book III (254:C 471; 257:C 474), that this opinion resembles the opinion of those who assume that there are gods and that their forms are like human ones. Hence the view expressed above is not a good one, because it leads us away from the truth insofar as it makes us think that it is possible for man to exist without flesh and bones, just as it is possible for a circle to exist without bronze, which clearly does not belong to the species of a circle.

             1519. But this case is not similar; for a man is not related to flesh and bones in the same way that a circle is related to bronze, because a circle is not something sensible in its own intelligible expression; for it can be understood without sensible matter. Hence, bronze, which is sensible matter, is not part of the species of a circle. But an animal seems to be a sensible thing since it cannot be defined without motion; for an animal is distinguished from something that is not an animal by means of sensation and motion, as is clear in Book I of The Soul. Therefore an animal cannot be defined without including bodily parts, which are disposed in a proper way for motion; for the hand is not a part of man when it exists in every state, but when it is disposed in such a way that it can perform the proper work of a hand; and this it cannot do without the soul, which is the principle of motion. Hence it is necessary that the hand be a part of man insofar as it is animated, but it is not a part of man insofar as it is not animated, like the hand of a corpse or that in a painting. Therefore such parts as are required for the carrying out of the proper operation of the species must be parts of the species; both those which pertain to the form and those which pertain to matter.

             1520. And with regard to (636).

             Next he answers the question with regard to the objects of mathematics; for though the solution has been given above with regard to natural things, it seems that the difficulty still remains with regard to the objects of mathematics; for he had said above that since an animal is sensible it cannot be defined without sensible parts, as a circle can be defined without bronze, which is sensible matter. Therefore "with regard to the objects of mathematics the question arises why the intelligible expressions of the parts," i.e., the definitions of the parts, "are not parts of the intelligible expression of the whole," e.g., why semicircles, or half-circles, are not given in the definition of a circle; for it cannot be said that these, namely, semicircles, are sensible things, as bronze is sensible matter.

             1521. But he answers that it makes no difference to his thesis whether the material parts are sensible or not; because there is intelligible matter even in things which are not sensible. And such matter--the kind which is not a part of the species--belongs to everything whose essence or species is not the same as itself "but is a particular thing," i.e., a determinate particular, as if to say that in everything which is not its own species but is a definite individual determined in species there must be certain material parts which are not parts of the species. For since Socrates is not identical with his own humanity but has humanity, for this reason he has in himself certain material parts which are not parts of his species but of this individual matter, which is the principle of individuation, for example, this flesh and these bones.

             1522. And, similarly, in this particular circle there are these particular lines which are not parts of the species. Hence it is clear that parts of this kind are not parts of the universal circle but of singular circles, as was stated above (627:C 1492). And for this reason semicircles are not included in the definition of the universal circle, because they are parts of singular circles and not of the universal circle. This is true both of sensible and intelligible matter; for matter is found in both modes, as is evident from what has been said. But if there were some individual which was the same as its own species, for example, if Socrates were his own humanity, there would be no parts in Socrates which would not be parts of humanity.

             1523. And it is also (637).

             He now sums up the solution given above by using animal as an example. He says that it is evident that the soul "is a primary substance," i.e., the form of animal, and that the body is matter, and that "man is the composite of both," i.e., insofar as they are taken universally; but that Socrates or Coriscus is the composite of both taken particularly, because "soul is taken in two senses," i.e., universally and particularly, as soul and as this soul. Hence what is signified as a whole must be taken both universally and singularly, in the way in which soul is taken in two senses, because this is in keeping with both views which men take of the soul. For, as was said above (624:C 1467), some claim that a man or an animal is its soul, whereas others say that a man or an animal is not its soul "but the whole," i.e., the composite of soul and body.

             1524. It is evident, then, according to the opinion which affirms that man is his soul, that the term soul is taken both universally and singularly, as soul and this soul; and the term man is also taken both universally and particularly, i.e., singularly, as man and as this man. And similarly, too, according to the opinion which affirms that man is a composite of body and soul, it follows that, if simple things may be taken both universally and singularly, composites may also be taken both universally and singularly; for example, if the soul is this thing and the body is this thing, which are referred to in an unqualified sense as parts of the composite, it follows that the terms universal and particular, or singular, may be applied not only to the parts but also to the composite.

             1525. But whether (638).

             He explains what still remains to be established about substances; and he gives the two issues which have to be dealt with. The first is this: when it has been established that the substance and whatness of sensible and material things are parts of the species, the next thing that has to be established is whether there is some substance besides the matter "of such substances," i.e., of material and sensible substances, so that it is necessary to look for some other substance of these sensible things besides the one which has been dealt with; as some affirm that there are numbers existing apart from matter, "or something of the kind," i.e., that separate Forms or Ideas are the substances of these sensible things. This must be investigated later on (Books XIII and XIV).

             1526. For this investigation is the one proper to this science, because in this science we attempt to establish something about sensible substances "for the sake of these," i.e., for the sake of immaterial substances, because the study of sensible and material substances belongs in a sense to the philosophy of nature, which is not first philosophy, but second philosophy, as was stated in Book IV (323:C 593). For first philosophy is concerned with the first substances, which are immaterial ones, which it studies not only inasmuch as they are substances but inasmuch as they are such substances, namely, inasmuch as they are immaterial. But it does not study sensible substances inasmuch as they are such substances but inasmuch as they are substances, or also beings, or inasmuch as we are led by such substances to a knowledge of immaterial substances. But the philosopher of nature, on the other hand, deals with material substances, not inasmuch as they are substances, but inasmuch as they are material and have a principle of motion within themselves.

             1527. And because someone might think that the philosophy of nature should not treat of material and sensible substances in their entirety, but only of their matters, he therefore rejects this, saying that the philosophy of nature must consider not only matter but also the part "which is intelligible," namely, the form. And it must also consider form more than matter, because form is nature to a greater degree than matter, as was proved in Book II of the Physics.

             1528. Second, it remains to be established how "the parts in the intelligible expression," i.e., in the definition, are disposed: whether they are parts of the substance actually. And it also remains to be established why the definition, when it is composed of many parts, is one intelligible expression; for it is evident that the definition of a thing must be only one intelligible expression, because a thing is one, and a definition signifies what a thing is. But how a thing having parts is one must be investigated later (733:C 1755).

             1529. We have stated (639).

             Next he sums up the points which have been established. He says that it has been stated what the essence of a thing is, and how it is predicated of all things, and that it is predicated essentially. And it has also been stated why the intelligible expression signifying the essence of some things contains in itself the parts of the thing defined, just as the definition of a syllable contains its letters, and "why that of others does not," as the definition of a circle does not contain semicircles. And again it has also been stated that those parts which are material parts of substance are not given "in the intelligible expression of substance," i.e., of form, because such parts are not "parts of that substance," i.e., of the form, but are parts of the whole composite.

             1530. Now in one sense there is a definition of this kind of composite, and in another sense there is not; for if it is taken "with matter," namely, the individual, there is no definition of it, since singulars are not defined, as was stated above (627:C 1493). The reason is that such individual matter is something unlimited and indeterminate; for matter is limited only by form. But if composite is taken "with reference to the primary substance," i.e., to form, it has a definition; for the composite is defined when taken specifically, but not when taken individually.

             1531. And just as the individual is individuated by matter, in a similar fashion each thing is placed in its proper species by its form; for man is man, not because he has flesh and bones, but because he has a rational soul in this flesh and these bones. It is necessary, then, that the definition of the species should be taken from the form, and that only those material parts should be given in the definition of the species, in which the form has the primary and chief role, as the intelligible expression of man is one which contains soul; for man is man because he has such a soul. And for this reason, if man is defined, he must be defined by his soul, yet in his definition one must include the parts of the body in which the soul is first present, such as the heart or the brain, as was said above (626:C 1489).

             1532. For the substance, of which matter is not a part, "is the specifying principle," i.e., the form, which is present in matter; and from this form and matter "the whole substance" is derived, i.e., made determinate and defined; for example, concavity is a form of this kind, for from this and from nose snubnose and snubness are derived. And in the same way man and humanity are derived from soul and body. For if nose, which plays the part of matter, were part of curvature, then when curved nose is referred to, the term nose would be expressed twice; for it is expressed once by its own name, and it is included again in the definition of the curved. However, this would be the case if nose were placed in the definition of the curved as part of the essence of curvature, and not by addition, as was stated above (624:C 1472). And even though matter is not present in the essence of form, it is nevertheless present in the whole composite substance; for example, curvature is present in snub nose, and individual matter is also present in Callias.

             1533. It was also said above (591:C 1362) that the essence of each thing is the same as the thing of which it is the essence. This is true without qualification in some cases, "as in the case of primary substances," i.e., in that of immaterial substances, just as curvature itself is the same as the essence of curvature, provided that curvature belongs to primary substances. He says this because curvature seems to be a form in matter, though not in sensible matter but in an intelligible matter--continuous quantity. Or, according to another text, "which is first"; for there is a primary curvature, like the curvature which exists among the separate Forms, according to the Platonists, and of these Forms it is universally true that each is the same as its own essence. But the other curvature which is present in sensible things or in the objects of mathematics is not a primary one. Hence it is not the same as its essence.

             1534. And in explaining this he says that he does not use the term primary substance here to mean a particular substance, as he does in the Categories, but to mean something which does not exist in something else "as in a subject or matter," i.e., those things which are not forms in matter, such as the separate substances. But all those which have the nature of matter or are conceived with matter, such as composites, which have matter in their intelligible expression, are not the same as their essence. Nor do those predications which are accidental form a unity, as Socrates and musician are the same accidentally.

             1535. Now it must be noted that from the opinion which he expressed here that each thing and its essence are the same, he now excludes two kinds of things: (1) things which are accidental, and (2) substances which are material, although above he excluded only those things which are said to be accidental. And it is necessary not only to exclude the former but also to exclude material substances; for, as was said above (622:C 1460), what the definition signifies is the essence, and definitions are not assigned to individuals but to species; and therefore individual matter, which is the principle of individuation, is distinct from the essence. But in reality it is impossible for a form to exist except in a particular substance. Hence if any natural thing has matter which is part of its species, and this pertains to its essence, it must also have individual matter, which does not pertain to its essence. Therefore, if any natural thing has matter, it is not its own essence but is something having an essence; for example, Socrates is not humanity but something having humanity. And if it were possible for a man to be composed of body and soul and not be this particular man composed of this body and this soul, he would still be his own essence, even though he contained matter.

             1536. Now even though man does not exist apart from singular men in reality, nevertheless man is separable in his intelligible expression, which pertains to the domain of logic. Therefore, above (578:C 1308), where he considered essence from the viewpoint of logic, he did not exclude material substances from being their own essence; for man as a universal is the same as his essence, logically speaking. And now having come to natural principles, which are matter and form, and having shown how they are related to the universal in different ways, and to the particular thing which subsists in nature, he now excludes material substances, which exist in reality, from the statement which he had made above to the effect that the essence of a thing is the same as the thing of which it is the essence. Moreover it follows that those substances which are subsistent forms alone do not have any principle individuating them which is extrinsic to the intelligible expression (of the thing or of the species) which signifies their whatness. Concerning these things, then, it is true that each is unqualifiedly the same as its own essence.