contraries in a prior sense. E.g., if white and black are contraries, and the one is a penetrative This is Plato's definition. Cf. Plat. Tim. 67d, e. and the other a compressive color, these differentiae, "penetrative" and "compressive," are prior, and so are opposed to each other in a prior sense. But it is the species which have contrary differentiae that are more truly contraries; the other, i.e.
intermediate, species will consist of genus and differentiae. E.g., all colors which are intermediate between white and black should be described by their genus (i.e. color) and by certain differentiae. But these differentiae will not be the primary contraries; otherwise every thing will be either white or black. Therefore they will be different from the primary contraries. Therefore they will be intermediate between them, and the primary differentiae will be "the penetrative" and "the compressive." Thus we must first investigate the contraries which are not contained in a genus, and discover of what their intermediates are composed. For things which are in the same genus must either be composed of differentiae which are not compounded with the genus, or be incomposite. Contraries are not compounded with one another, and are therefore first principles; but intermediates are either all incomposite or none of them. Now from the contraries something is generated in such a way that change will reach it before reaching the contraries themselves (for there must be something which is less in degree than one contrary and greater than the other). Therefore this also will be intermediate between the contraries. Hence all the other intermediates must be composite; for that which is greater in degree than one contrary and less than the other is in some sense a compound of the contraries of which it is said to be greater in degree than one and less than the other. And since there is nothing else homogeneous which is prior to the contraries, all intermediates must be composed of contraries. Therefore all the lower terms, both contraries and intermediates, must be composed of the primary contraries. Thus it is clear that intermediates are all in the same genus, and are between contraries, and are all composed of contraries. That which is "other in species" than something else is "other" in respect of something and that something must apply to both. E.g., if an animal is other in species than something else, they must both be animals. Hence things which are other in species must be in the same genus. The sort of thing I mean by "genus" is that in virtue of which two things are both called the same one thing; and which is not accidentally differentiated, whether regarded as matter or otherwise. For not only must the common quality belong to both, e.g., that they are both animals, but the very animality of each must be different; e.g., in one case it must be equinity and in the other humanity. Hence the common quality must for one be other in species than that which it is for the other. They must be, then, of their very nature, the one this kind of animal, and the other that; e.g., the one a horse and the other a man. Therefore this difference must be "otherness of genus" (I say "otherness of genus" because by "difference of genus" I mean an otherness which makes the genus itself other); this, then, will be a form of contrariety. This is obvious by induction. Aristotle does not use induction to prove his point; indeed he does not prove it at all. For all differentiation is by opposites, and we have shown In ch. 4. that contraries are in the same genus, because contrariety was shown to be complete difference. But difference in species is always difference from something in respect of something; therefore this is the same thing, i.e. the genus, for both. (Hence too all contraries which differ in species but not in genus are in the same line of predication, Or "category." and are other than each other in the highest degree; for their difference is complete, and they cannot come into existence simultaneously.) Hence the difference is a form of contrariety. To be "other in species," then, means this: to be in the same genus and involve contrariety, while being indivisible (and "the same in species" applies to all things which do not involve contrariety, while being indivisible); for it is in the course of differentiation and in the intermediate terms that contrariety appears, before we come to the indivisibles. i.e., indivisible species and individuals.
Thus it is evident that in relation to what is called genus no species is either the same or other in species (and this is as it should be, for the matter is disclosed by negation, and the genus is the matter of that of which it is predicated as genus; not in the sense in which we speak of the genus or clan of the Heraclidae, Cf. Aristot. Met.
5.28.1. but as we speak of a genus in nature); nor yet in relation to things which are not in the same genus. From the latter it will differ in genus, but in species from things which are in the same genus. For the difference of things which differ in species must be a contrariety; and this belongs only to things which are in the same genus. The question might be raised as to why woman does not differ in species from man, seeing that female is contrary to male, and difference is contrariety; and why a female and a male animal are not other in species, although this difference belongs to "animal" per se, and not as whiteness or blackness does; "male" and "female" belong to it qua animal. This problem is practically the same as "why does one kind of contrariety (e.g. "footed" and "winged") make things other in species, while another (e.g. whiteness and blackness) does not?" The answer may be that in the one case the attributes are peculiar to the genus, and in the other they are less so; and since one element is formula and the other matter, contrarieties in the formula produce difference in species, but contrarieties in the concrete whole do not. Hence the whiteness or blackness of a man does not produce this, nor is there any specific difference between a white man and a black man; not even if one term is assigned to each. For we are now regarding "man" as matter, and matter does not produce difference; and for this reason, too, individual men are not species of "man," although the flesh and bones of which this and that man consist are different. The concrete whole is "other," but not "other in species," because there is no contrariety in the formula, and this is the ultimate indivisible species. But Callias is definition and matter. Then so too is "white man," because it is the individual, Callias, who is white. Hence "man" is only white accidentally. Again, a bronze circle and a wooden one do not differ in species; and a bronze triangle and a wooden circle differ in species not because of their matter, but because there is contrariety in their formulae. But does not matter, when it is "other" in a particular way, make things "other in species"? Probably there is a sense in which it does. Otherwise why is this particular horse "other in species" than this particular man, although the definitions involve matter? Surely it is because there is contrariety in the definition, for so there also is in "white man" and "black horse"; and it is a contrariety in species, but not because one is white and the other black; for even if they had both been white, they would still be "other in species." "Male" and "female" are attributes peculiar to the animal, but not in virtue of its substance; they ar material or physical. Hence the same semen may, as the result of some modification, become either female or male. We have now stated what "to be other in species" means, and why some things differ in species and others do not. Since contraries are other in form, It appears that in this chapter (apart from 5, which may be a later addition) the terms EI)=DOS and GE/NOS are used in a non-technical sense. Cf.
Ross on Aristot. Met. 1058b 28. and "the perishable" and "imperishable" are contraries (for privation is a definite incapacity), "the perishable" must be "other in kind" than "the imperishable." But so far we have spoken only of the universal terms; and so it might appear to be unnecessary that anything perishable and imperishable should be "other in form," just as in the case of white and black. For the same thing may be both at the same time, if it is a universal (e.g, "man" may be both white and black); and it may still be both if it is a particular, for the same person may be white and black, although not at the same time. Yet white is contrary to black. But although some contraries (e.g. those which we have just mentioned, and many others) can belong to certain things accidentally, others cannot; and this applies to "the perishable" and "the imperishable." Nothing is accidentally perishable; for that which is accidental may not be applicable; but perishability is an attribute which applies necessarily when it is applicable at all.
Otherwise one and the same thing will be imperishable as well as perishable, if it is possible for perishability not to apply to it. Thus perishability must be either the substance or in the substance of every perishable thing. The same argument also applies to the imperishable; for both perishability and imperishability are attributes which are necessarily applicable. Hence the characteristics in respect of which and in direct consequence of which one thing is perishable and another imperishable are opposed; and therefore they must be other in kind. Thus it is obvious that there cannot be Forms such as some thinkers maintain; for then there would be both a perishable and an imperishable "man." i.e., the individual man is perishable and the Idea of man imperishable; and these must be other in kind ( GE/NEI non-technical). But the Platonists hold that the Idea is the same in species as the particular. This is impossible if it is other in genus ( GE/NEI technical). Yet the Forms are said to be the same in species as the particulars, and not merely to share a common predicate with them; but things which are other in genus differ more widely than things which are other in species.
That wisdom is a science of first principles is clear from our Introductory remarks, Aristot. Met.
1.3-10. in which we of raised objections to the statements of other thinkers about the first principles. It might be asked, however, whether we should regard Wisdom as one science or as more than one. Cf. Aristot. Met. 3.1.5, Aristot. Met.
3.2.1-10. If as one, it may be objected that the objects of one science are always contraries; but the first principles are not contraries. And if it is not one, what sort of sciences are we to suppose them to be? Again, is it the province of one science, or of more than one, to study the principles of demonstration? Cf. Aristot. Met. 3.1.5,, Aristot.
Met. 3.2.10-15, where the problem takes a slightly different form. If of one, why of it rather than of any other? And if of more than one, of what sort are we to suppose them to be? Again, are we to suppose that Wisdom deals with all substances or not? Cf. Aristot. Met. 3.1.6, Aristot. Met. 3.2.15-17. If not with all, it is hard to lay down with what kind it does deal; while if there is one science of them all, it is not clear how the same science can deal with more than one subject. Again, is this science concerned only with substances, or with attributes as well? Cf. Aristot. Met. 3.1.8-10, Aristot. Met.
3.2.18-19. For if it is a demonstration of attributes, it is not concerned with substances; and if there is a separate science of each, what is each of these sciences, and which of them is Wisdom? qua demonstrative, the science of attributes appears to be Wisdom; but qua concerned with that which is primary, the science of substances. Nor must we suppose that the science which we are seeking is concerned with the causes described in the Physics. Aristot. Physics 2.3. It is not concerned with the final cause; for this is the Good, and this belongs to the sphere of action and to things which are in motion; and it is this which first causes motion (for the end is of this nature); but there is no Prime Mover in the sphere of immovable things. And in general it is a difficult question whether the science which we are now seeking is concerned with sensible substances, or not with sensible substances, but with some other kind. Cf. Aristot. Met. 3.1.7, Aristot.
Met.3.2.20-30. If with another kind, it must be concerned either with the Forms or with mathematical objects. Now clearly the Forms do not exist. (But nevertheless, even if we posit them, it is a difficult question as to why the same rule does not apply to the other things of which there are Forms as applies to the objects of mathematics. I mean that they posit the objects of mathematics as intermediate between the Forms and sensible things, as a third class besides the Forms and the things of our world; but there is no "third man" This phrase has no technical sense here; cf. Aristot. Met. 1.9.4.
or "horse" besides the Ideal one and the particulars. If on the other hand it is not as they make out, what sort of objects are we to suppose to be the concern of the mathematician? Not surely the things of our world; for none of these is of the kind which the mathematical sciences investigate.) Nor indeed is the science which we are now seeking concerned with the objects of mathematics; for none of them can exist separately. But it does not deal with sensible substances either; for they are perishable. In general the question might be raised, to what science it pertains to discuss the problems concerned with the matter i.e., intelligible matter (cf. Aristot. Met. 7.10.18 ). This problem is not raised in Book 3. of mathematical objects. It is not the province of physics, because the whole business of the physicist is with things which contain in themselves a principle of motion and rest; nor yet of the science which inquires into demonstration and scientific knowledge, for it is simply this sort of thing which forms the subject of its inquiry. It remains, therefore, that it is the science which we have set ourselves to find that treats of these subjects. One might consider the question whether we should regard the science which we are now seeking as dealing with the principles which by some are called elements. Cf. Aristot. Met.
3.1.10, Aristot. Met.
3.3. But everyone assumes that these are present in composite things; and it would seem rather that the science which we are seeking must be concerned with universals, since every formula and every science is of universals and not of ultimate species; so that in this case it must deal with the primary genera. These would be Being and Unity; for these, if any, might best be supposed to embrace all existing things, and to be most of the nature of first principles, because they are by nature primary; for if they are destroyed, everything else is destroyed with them, since everything exists and is one. But inasmuch as, if Being and Unity are to be regarded as genera, they must be predicable of their differentiae, whereas no genus is predicable of any of its differentiae, from this point of view it would seem that they should be regarded neither as genera nor as principles. Further, since the more simple is more nearly a principle than the less simple, and the ultimate subdivisions of the genus are more simple than the genera (because they are indivisible), and the genera are divided into a number of different species, it would seem that species are more nearly a principle than genera. On the other hand, inasmuch as species are destroyed together with their genera, it seems more likely that the genera are principles; because that which involves the destruction of something else is a principle. These and other similar points are those which cause us perplexity. Again, ought we to assume the existence of something else besides particular things, or are they the objects of the science which we are seeking? Cf. Aristot. Met. 3.1.11, Aristot.
Met. 3.4.1-8. It is true that they are infinite in number; but then the things which exist besides particulars are genera or species, and neither of these is the object of the science which we are now seeking. We have explained Aristot. Met. 11.1.11-13 why this is impossible. Indeed, in general it is a difficult question whether we should suppose that there is some substance which exists separately besides sensible substances (i.e. the substances of our world), or that the latter constitute reality, and that it is with them that Wisdom is concerned. It seems that we are looking for some other kind of substance, and that this is the object of our undertaking: I mean, to see whether there is anything which exists separately and independently, and does not appertain to any sensible thing. But again, if there is another kind of substance besides sensible substances, to what kind of sensible things are we to suppose that it corresponds?
Why should we suppose that it corresponds to men or horses rather than to other animals, or even to inanimate objects in general? And yet to manufacture a set of eternal substances equal in number to those which are sensible and perishable would seem to fall outside the bounds of plausibility. Yet if the principle which we are now seeking does not exist in separation from bodies, what can we suppose it to be if not matter? Yes, but matter does not exist actually, but only potentially. It might seem rather that a more appropriate principle would be form or shape; but this is perishable Forms which are induced in matter are perishable, although not subject to the process of destruction; they are at one time and are not at another (cf. Aristot. Met.
7.15.1 ). The only pure form (i.e., the only form which is independent of matter in any and every sense) is the prime mover ( Aristot. Met.
12.7 ).; and so in general there is no eternal substance which exists separately and independently. But this is absurd, because it seems natural that there should be a substance and principle of this kind, and it is sought for as existing by nearly all the most enlightened thinkers.
For how can there be any order in the universe if there is not something eternal and separate and permanent? Again, if there is a substance and principle of such a nature as that which we are now seeking, and if it is one for all things, i.e. the same for both eternal and perishable things, it is a difficult question as to why, when the principle is the same, some of the things which come under that principle are eternal, and others not; for this is paradoxical. Cf. Aristot. Met. 3.1.12, Aristot.
Met. 3.4.11-23. But if there is one principle of perishable things, and another of eternal things, if the principle of perishable things is also eternal, we shall still have the same difficulty; because if the principle is eternal, why are not the things which come under that principle eternal? And if it is perishable, it must have another principle behind it, and that principle must have another behind it; and the process will go on to infinity. On the other hand, if we posit the principles which seem most unchangeable, Being and Unity, Cf. Aristot. Met. 3.1.13, Aristot. Met.
3.4.24-34. (a) unless each of them denotes a particular thing and a substance, how can they be separate and independent? but the eternal and primary principles for which we are looking are of this nature. (b) If, however, each of them denotes a particular thing and a substance, then all existing things are substances; for Being is predicated of everything, and Unity also of some things. But that all things are substances is false. (c) As for those who maintain that Unity is the first principle and a substance, and who generate number from Unity and matter as their first product, and assert that it is a substance, how can their theory be true? How are we to conceive of 2 and each of the other numbers thus composed, as one? On this point they give no explanation; nor is it easy to give one. But if we posit lines or the things derived from them (I mean surfaces in the primary sense i.e., intelligible surfaces, etc. ) as principles, Cf. Aristot. Met.
3.1.15, Aristot. Met.
3.5. these at least are not separately existing substances, but sections and divisions, the former of surfaces and the latter of bodies (and points are sections and divisions of lines); and further they are limits of these same things.
All these things are integral parts of something else, and not one of them exists separately. Further, how are we to suppose that there is a substance of unity or a point? for in the case of every substance sc. which is liable to generation or destruction. there is a process of generation, but in the case of the point there is not; for the point is a division. It is a perplexing fact also that whereas every science treats of universals and types, substance is not a universal thing, but rather a particular and separable thing; so that if there is a science that deals with first principles, how can we suppose that substance is a first principle? Cf. Aristot. Met. 3.1.14, Aristot. Met. 3.6.7-9. Again, is there anything besides the concrete whole (I mean the matter and the form in combination) or not? This section belongs to the problem discussed in 1-5 above. If not, all things in the nature of matter are perishable; but if there is something, it must be the form or shape.
It is hard to determine in what cases this is possible and in what it is not; for in some cases, e.g. that of a house, the form clearly does not exist in separation. Again, are the first principles formally or numerically the same? Cf. Aristot. Met.
3.1.12, Aristot. Met.
3.4.8-10. If they are numerically one, all things will be the same. Since the science of the philosopher is concerned with Being qua Being universally, This chapter corresponds to Aristot. Met. 4.1, 2, with which it should be compared. and not with some part of it, and since the term Being has several meanings and is not used only in one sense, if it is merely equivocal and has no common significance it cannot fall under one science (for there is no one class in things of this kind); but if it has a common significance it must fall under one science. Now it would seem that it is used in the sense which we have described, like "medical" and "healthy," for we use each of these terms in several senses; and each is used in this way because it has a reference, one to the science of medicine, and another to health, and another to something else; but each refers always to the same concept. A diagnosis and a scalpel are both called medical, because the one proceeds from medical science and the other is useful to it. The same is true of "healthy"; one thing is so called because it is indicative, and another because it is productive, of health; and the same applies to all other cases. Now it is in this same way that everything which exists is said to be; each thing is said to be because it is a modification or permanent or temporary state or motion or some other such affection of Being qua Being. And since everything that is can be referred to some one common concept, each of the contrarieties too can be referred to the primary differentiae and contrarieties of Being—whether the primary differentiae of Being are plurality and unity, or similarity and dissimilarity, or something else; for we may take them as already discussed. Cf. Aristot. Met.
4.2.9 n. It makes no difference whether that which is is referred to Being or Unity; for even if they are not the same but different, they are in any case convertible, since that which is one also in a sense is, and that which is is one. Now since the study of contraries pertains to one and the same science, and each contrary is so called in virtue of privation (although indeed one might wonder in what sense they can be called contraries in virtue of privation when they admit of a middle term—e.g. "unjust" and "just"), in all such cases we must regard the privation as being not of the whole definition but of the ultimate species. E.g., if the just man is "one who is obedient to the laws in virtue of some volitional state," the unjust man will not be entirely deprived of the whole definition, but will be "one who is in some respect deficient in obedience to the laws"; and it is in this respect that the privation of justice will apply to him (and the same holds good in all other cases). And just as the mathematician makes a study of abstractions (for in his investigations he first abstracts everything that is sensible, such as weight and lightness, hardness and its contrary, and also heat and cold and all other sensible contrarieties, leaving only quantity and continuity—sometimes in one, sometimes in two and sometimes in three dimensions—and their affections qua quantitative and continuous, and does not study them with respect to any other thing; and in some cases investigates the relative positions of things and the properties of these, and in others their commensurability or incommensurability, and in others their ratios; yet nevertheless we hold that there is one and the same science of all these things, viz.
geometry), so it is the same with regard to Being. For the study of its attributes in so far as it is Being, and of its contrarieties i.e., identity, otherness, etc.
qua Being, belongs to no other science than Philosophy; for to physics one would assign the study of things not qua Being but qua participating in motion, while dialectics and sophistry deal with the attributes of existing things, but not of things qua Being, nor do they treat of Being itself in so far as it is Being. Therefore it remains that the philosopher is the man who studies the things which we have described, in so far as they are Being. And since everything that is, although the term has several meanings, is so described in virtue of some one common concept, and the same is true of the contraries (since they can be referred to the primary contrarieties and differences of Being), and since things of this kind can fall under one science, the difficulty which we stated at the beginning Aristot. Met. 11.1.1. may be regarded as solved Also the problem stated in ch. i. 3. —I mean the problem as to how there can be one science of several things which are different in genus. Since even the mathematician uses the common axioms only in a particular application, it will be the province of Primary Philosophy to study the principles of these as well. This chapter corresponds to Aristot. Met. 4.3.1-6, and answers the problem stated in Aristot. Met. 11.1.2. That when equals are taken from equals the remainders are equal is an axiom common to all quantities; but mathematics isolates a particular part of its proper subject matter and studies it separately; e.g. lines or angles or numbers or some other kind of quantity, but not qua Being, but only in so far as each of them is continuous in one, two or three dimensions. But philosophy does not investigate particular things in so far as each of them has some definite attribute, but studies that which is, in so far as each particular thing is . The same applies to the science of physics as to mathematics, for physics studies the attributes and first principles of things qua in motion, and not qua Being; but Primary Science, as we have said, deals with these things only in so far as the subjects which underlie them are existent, and not in respect of anything else. Hence we should regard both physics and mathematics as subdivisions of Wisdom. There is a principle in existing things about which we cannot make a mistake This chapter corresponds to Aristot. Met. 4.3.7-4.31.; of which, on the contrary, we must always realize the truth—viz. that the same thing cannot at one and the same time be and not be, nor admit of any other similar pair of opposites. Of such axioms although there is a proof ad hominem, there is no absolute proof; because there is no principle more convincing than the axiom itself on which to base an argument, whereas there must be such a principle if there is to be absolute proof. But he who wants to convince an opponent who makes opposite statements that he is wrong must obtain from him an admission which shall be identical with the proposition that the same thing cannot at one and the same time be and not be, but shall seem not to be identical with it. This is the only method of proof which can be used against one who maintains that opposite statements can be truly made about the same subject. Now those who intend to join in discussion must understand one another to some extent; for without this how can there be any common discussion between them? Therefore each of the terms which they use must be intelligible and signify something; not several things, but one only; or if it signifies more than one thing, it must be made clear to which of these the term is applied. Now he who says that A is and is not denies what he asserts, and therefore denies that the term signifies what it does signify. But this is impossible.
Therefore if "to be so-and-so" has a definite meaning, the opposite statement about the same subject cannot be true. Again, if the term has a definite significance and this is truly stated, it must of necessity be so. sect. 6= Aristot. Met. 4.4.14-16. But that which of necessity is can never not be. Hence opposite statements about the same subject cannot be true. Again, if the assertion is no more true than the negation, it will be no more true to say "A is man" than to say "A is not man." With this section cf. Aristot. Met. 4.4.26-30. But it would also be admitted that it is more or at least not less true to say that a man is not a horse than to say that he is not a man; and therefore, since it was assumed that opposite statements are equally true, it will be true to say that the same person is also a horse. It follows therefore, that the same person is a man and a horse, or any other animal. Thus, although there is no absolute proof of these axioms, there is an ad hominem proof where one's opponent makes these assumptions. sect. 8= Aristot. Met. 4.3.10. Perhaps even Heraclitus himself, if he had been questioned on these lines, would have been compelled to admit that opposite statements can never be true of the same subjects; as it is, he adopted this theory through ignorance of what his doctrine implied. In general, sect. 9-11= Aristot. Met.
4.4.31. if what he says is true, not even this statement itself (I mean "that the same thing can at one and the same time be and not be") will be true; because just as, when they are separated, the affirmation is no more true than the negation, so in the same way, if the complex statement is taken as a single affirmation, the negation will be just as true as the whole statement regarded as an affirmation. And further, if nothing can be truly affirmed, then this very statement—that there is no such thing as a true affirmation—will be false. But if there is such a thing, the contentions of those who raise objections of this kind and utterly destroy rational discourse may be considered to be refuted. Cf. Aristot. Met.
4.8.4, 5. Very similar to the views which we have just mentioned is the dictum of Protagoras This chapter forms a summary of Aristot. Met.
4.5-8. sect. 1-3= Aristot. Met.
4.5.1-5.; for he said that man is the measure of all things, by which he meant simply that each individual's impressions are positively true. But if this is so, it follows that the same thing is and is not, and is bad and good, and that all the other implications of opposite statements are true; because often a given thing seems beautiful to one set of people and ugly to another, and that which seems to each individual is the measure. This difficulty will be solved if we consider the origin of the assumption. It seems probable that it arose in some cases from the doctrine of the natural philosophers, and in others from the fact that everyone does not form the same opinion about the same things, but to some a given thing seems sweet and to others the contrary. For that nothing comes from what is not, but everything from what is, is a doctrine common to nearly all natural philosophers. With sect. 4, 5 cf. Aristot. Met. 4.5.6. Since, then, a thing does not become white which was before completely white and in no respect not-white, that which becomes white must come from what was not-white. Hence according to this theory there would be generation from what is not, unless the same thing were originally white and not-white. However, it is not hard to solve this difficulty. We have explained in the Physics Aristot. Physics 1.7-9. in what sense things which are generated are generated from what is not, and in what sense from what is. But to attach equal importance to the opinions and impressions of opposing parties is foolish, because clearly one side or the other must be wrong. sect. 5-7= Aristot.
Met. 4.5.23-27. This is evident from what happens in the sphere of sensation; for the same thing never seems to some people sweet and to others to the contrary unless one of the parties has the organ of sense which distinguishes the said flavors injured or impaired. Such being the case, the one party should be taken as the "measure," and the other not. And I hold the same in the case of good and bad, and of beautiful and ugly, and of all other such qualities. For to maintain this view i.e., that the same thing has contrary qualities. is just the same as to maintain that what appears to us when we press the finger below the eye and make a thing seem two instead of one must be two because it appears to be so, and then afterwards that it must be one; because if we do not interfere with our sight that which is one appears to be one. And in general it is absurd to form our opinion of the truth from the appearances of things in this world of ours which are subject to change and never remain in the same state sect.
22.; for it is by reference to those things which are always the same state and undergo no change that we should prosecute our search for truth. Of this kind are the heavenly bodies; for these do not appear to be now of one nature and subsequently of another, but are manifestly always the same and have no change of any kind. Again, if there is motion there is also something which is moved; and everything is moved from something and into something. Therefore that which is moved must be in that from which it is to be moved, and must also not be in it; and must be moved into so-and-so and must also come to be in it; but the contradictory statements cannot be true at the same time, as our opponents allege. And if the things of our world are in a state of continuous flux and motion in respect of quantity, and we assume this although it is not true, why should they not be constant in respect of quality? Cf. Aristot. Met. 4.5.20, 21. It appears