by Aristotle
[103b1] 8 · Of sameness then, as has been said, three types are to be distinguished. Now one way to confirm that the elements mentioned above are those out of which and through which and to which arguments proceed, is by induction; for if any one were to survey propositions and problems one by one, it would be seen that each was [5] formed either from the definition of something or from its property or from its genus or from its accident. Another way to confirm it is through deduction. For every predicate of a subject must of necessity be either convertible with its subject or not: and if it is convertible, it would be its definition or property, for if it signifies [10] the essence, it is the definition; if not, it is a property—for this was what a property is, viz. what is predicated convertibly, but does not signify the essence. If, on the other hand, it is not predicated convertibly of the thing, it either is or is not one of the terms contained in the definition of the subject; and if it is one of those terms, then it will be the genus or the differentia, inasmuch as the definition consists of [15] genus and differentiae; whereas, if it is not one of those terms, clearly it would be an accident, for accident was said to be what belongs to a subject without being either its definition or its genus or a property.
[20] 9 · Next, then, we must distinguish between the categories of predication in which the four above-mentioned are found. These are ten in number: What a thing is, Quantity, Quality, Relation, Place, Time, Position, State, Activity, Passivity. For the accident and genus and property and definition of anything will always be in one [25] of these predications; for all the propositions found through these signify either what something is or its quality or quantity or some one of the other types of predicate. It is clear, too, on the face of it that the man who signifies what something is signifies sometimes a substance, sometimes a quality, sometimes some one of the other types of predicate. For when a man is set before him and he says [30] that what is set there is a man or an animal, he states what it is and signifies a substance; but when a white colour is set before him and he says that what is set there is white or is a colour, he states what it is and signifies a quality. Likewise, also, if a magnitude of a cubit be set before him and he says that what is set there is a cubit or a magnitude, he will be describing what it is and signifying a quantity. [35] Likewise, also, in the other cases; for each of these kinds of predicate, if either it be asserted of itself, or its genus be asserted of it, signifies what something is; if, on the other hand, one kind of predicate is asserted of another kind, it does not signify what something is, but a quantity or a quality or one of the other kinds of predicate. Such, then, and so many, are the subjects on which arguments take place, and the materials with which they start. How we are to acquire them, and by what means [104a1] we are to become well supplied with them, falls next to be told.
10 · First, then, a definition must be given of a dialectical proposition and a dialectical problem. For it is not every proposition nor yet every problem that is to [5] be set down as dialectical; for no one in his senses would make a proposition of what no one holds, nor yet make a problem of what is obvious to everybody; for the latter admits of no doubt, while to the former no one would assent.
Now a dialectical proposition consists in asking something that is reputable to all men or to most men or to the wise, i.e. either to all, or to most, or to the most [10] notable of these, provided it is not paradoxical; for a man would probably assent to the view of the wise, if it be not contrary to the opinions of most men. Dialectical propositions also include views which are like those which are reputable; also propositions which contradict the contraries of opinions that are taken to be reputable, and also all opinions that are in accordance with the recognized arts. [15] Thus, supposing it to be reputable that the knowledge of contraries is the same, it might probably pass for reputable also that the perception of contraries is the same; also, supposing it to be a reputable opinion that there is but one single science of grammar, it might pass for a reputable opinion that there is but one science of flute-playing as well—and if more than one science of grammar, more than one science of flute-playing as well; for all these seem to be alike and akin. Likewise, [20] also, propositions contradicting the contraries of reputable opinions will pass as reputable; for if it is a reputable opinion that one ought to do good to one’s friends, it will also be a reputable opinion that one ought not to do them harm. Here, that one ought to do harm to one’s friends is the contrary, and that one ought not to do them harm is the contradictory of that contrary. Likewise also, if one ought to do good to [25] one’s friends, one ought not to do good to one’s enemies: this too is the contradictory of the contrary—the contrary being that one ought to do good to one’s enemies. Likewise, also, in other cases. Also, on comparison, it will look like a reputable opinion that the contrary predicate belongs to the contrary subject: e.g. if one ought to do good to one’s friends, one ought also to do evil to one’s enemies. (It might appear as if doing good to one’s friends were a contrary to doing evil to one’s [30] enemies; but whether this actually is or is not so in reality will be stated in the course of the discussion of contraries.)2 Clearly also, all opinions that are in accordance with the arts are dialectical propositions; for people are likely to assent to the views held by those who have made a study of these things, e.g. on a question of medicine [35] they will agree with the doctor, and on a question of geometry with the geometrician; and likewise also in other cases.
11 · A dialectical problem is a subject of inquiry that contributes either to [104b1] choice and avoidance, or to truth and knowledge, and does that either by itself, or as a help to the solution of some other such problem. It must, moreover, be something on which either people hold no opinion either way, or most people hold a contrary [5] opinion to the wise, or the wise to most people, or each of them among themselves. For some problems it is useful to know only with a view to choice or avoidance, e.g. whether pleasure is to be chosen or not, while some it is useful to know merely with a view to knowledge, e.g. whether the universe is eternal or not; others, again, are not useful in themselves for either of these purposes, but yet help us in regard to some [10] such problems; for there are many things which we do not wish to know in themselves, but for the sake of other things, in order that through them we may come to know something else. Problems also include questions in regard to which deductions conflict (the difficulty then being whether so-and-so is so or not, there being convincing arguments for both views); others also in regard to which we have [15] no argument because they are so vast, and we find it difficult to give our reasons, e.g. the question whether the universe is eternal or no; for into questions of that kind too it is possible to inquire.
Problems, then, and propositions are to be defined as aforesaid. A thesis is a [20] paradoxical belief of some eminent philosopher; e.g. the view that contradiction is impossible, as Antisthenes said; or the view of Heraclitus that all things are in motion; or that what exists is one, as Melissus says; for to take notice when any ordinary person expresses views contrary to men’s usual opinions would be silly. Or it may be a view contrary to men’s usual opinions about which we have an argument, e.g. the view maintained by the sophists that what is need not in every [25] case either have come to be or be eternal; for a musician who is a grammarian is so without ever having come to be so, or being so eternally. For even if some do not accept this view, a man might do so on the ground that it has an argument in its favour.
Now a thesis also is a problem, though a problem is not always a thesis, [30] inasmuch as some problems are such that we have no opinion about them either way. That a thesis is a problem, is clear; for it follows of necessity from what has been said that either the mass of men disagree with the wise about the thesis, or that the one or the other class disagree among themselves, seeing that the thesis is a [35] paradoxical belief. Practically all dialectical problems indeed are now called theses. But it should make no difference whichever description is used; for our object in thus distinguishing them has not
been to create a terminology, but to recognize [105a1] what differences actually exist between them.
Not every problem, nor every thesis, should be examined, but only one which might puzzle one of those who need argument, not punishment or perception. For [5] people who are puzzled to know whether one ought to honour the gods and love one’s parents or not need punishment, while those who are puzzled to know whether snow is white or not need perception. The subjects should not border too closely upon the sphere of demonstration, nor yet be too far removed from it; for the former cases admit of no doubt, while the latter involve difficulties too great for the art of the trainer.
[10] 12 · Having made these distinctions, we must distinguish how many species there are of dialectical arguments. There are induction and deduction. Now what deduction is has been said before; induction is a passage from particulars to universals, e.g. the argument that supposing the skilled pilot is the most effective, and likewise the skilled charioteer, then in general the skilled man is the best at his [15] particular task. Induction is more convincing and clear: it is more readily learnt by the use of the senses, and is applicable generally to the mass of men; but deduction is more forcible and more effective against contradictious people.
13 · The classes, then, of things about which, and of things out of which, [20] arguments are constructed, are to be distinguished in the way we have said before. The instruments whereby we are to become well supplied with deductions are four: one, the securing of propositions; second, the power to distinguish in how many ways an expression is used; third, the discovery of the differences of things; fourth, the investigation of likeness. The last three, as well, are in a certain sense propositions; [25] for it is possible to make a proposition corresponding to each of them, e.g. that the desirable is either the honourable or the pleasant or the expedient; and that sensation differs from knowledge in that the latter may be recovered again after it has been lost, while the former cannot; and that the relation of the healthy to health [30] is like that of the vigorous to vigour. The first proposition depends upon the use of one term in several ways, the second upon the differences of things, the third upon their likenesses.
14 · Propositions should be selected in as many ways as we drew distinctions in regard to the proposition: thus one may choose the opinions held by all or by most [35] men or by the wise, i.e. by all, or most, or the most notable of them—if they are not contrary to those that seem to be generally held; and, again, all opinions that are in accordance with the arts. We must make propositions also of the contradictories of [105b1] opinions contrary to those that seem to be generally held, as was laid down before. It is useful also to make them by selecting not only those opinions that actually are reputable, but also those that are like these, e.g. that the perception of contraries is the same—the knowledge of them being so—and that we see by admission of [5] something into ourselves, not by an emission; for so it is, too, in the case of the other senses; for in hearing we admit something into ourselves; we do not emit; and we taste in the same way. Likewise also in the other cases. Moreover, all statements [10] that seem to be true in all or in most cases, should be taken as a principle or accepted thesis; for they are posited by those who do not also see what exception there may be. We should select also from the written handbooks of argument, and should draw up sketch-lists of them upon each several kind of subject, putting them down under separate headings, e.g. ‘On Good’, or ‘On Life’—and that ‘On Good’ should deal with every form of good, beginning with the essence. In the margin, too, one should [15] indicate also the opinions of individual thinkers, e.g. that Empedocles said that the elements of bodies were four; for any one might assent to the saying of some reputable authority.
Of propositions and problems there are—to comprehend the matter in outline—three divisions; for some are ethical propositions, some are on natural [20] science, while some are logical. Propositions such as the following are ethical, e.g. ‘Ought one rather to obey one’s parents or the laws, if they disagree?’; such as this are logical, e.g. ‘Is the knowledge of opposites the same or not?’; while such as this [25] are on natural science, e.g. ‘Is the universe eternal or not?’ Likewise also with problems. The nature of each of the aforesaid kinds of proposition is not easily rendered in a definition, but we have to try to recognize each of them by means of the familiarity attained through induction, examining them in the light of the illustrations given above.
[30] For purposes of philosophy we must treat of these things according to their truth, but for dialectic only with an eye to opinion.
All propositions should be taken in their most universal form; then, the one should be made into many. E.g. ‘The knowledge of opposites is the same’; next, ‘The knowledge of contraries is the same’, and ‘of relative terms’. In the same way these [35] should again be divided, as long as division is possible, e.g. the knowledge of good and evil, of white and black, of cold and hot. Likewise also in other cases.
[106a1] 15 · On the subject of propositions, the above remarks are enough. As regards the number of ways in which a term is used, we must not only treat of those terms which are used in different ways, but we must also try to render their definitions; e.g. we must not merely say that justice and courage are called good in [5] one way, and that what conduces to vigour and what conduces to health are called so in another, but also that the former are so called because of a certain intrinsic quality they themselves have, the latter because they are productive of a certain result and not because of any intrinsic quality in themselves. Similarly also in other cases.
Whether a term is used in many ways or in one only, may be considered by the [10] following means. First, look and see if its contrary is used in many ways, whether the discrepancy between them be one of kind or one of names. For in some cases a difference is at once displayed even in the names; e.g. the contrary of sharp in the case of a sound is flat, while in the case of a body it is dull. Clearly, then, the [15] contrary of sharp is used in many ways, and if so, so also is sharp; for corresponding to each of the former terms the contrary will be different. For sharp will not be the same when contrary to dull and to flat, though sharp is the contrary of each. Again that in the case of a sound has sharp as its contrary, but in the case of a body raised,3 so that that is used in many ways, inasmuch as its contrary also is so used. Likewise, [20] also, fine as applied to an animal has ugly as its contrary, but, as applied to a house, mean; so that fine is homonymous.
In some cases there is no discrepancy of any sort in the names used, but a [25] difference of kind is at once obvious: e.g. in the case of clear and obscure;4 for sound is called clear and obscure, just as colour is too. As regards the names, then, there is no discrepancy, but the difference in kind is at once obvious; for colour is not called clear in a like way to sound. This is plain also through sensation; for of things that are the same in kind we have the same sense, whereas we do not judge clearness by [30] the same sense in the case of sound and of colour, but in the latter case we judge by sight, in the former by hearing. Likewise also with sharp and dull in regard to flavours and bodies: here in the latter case we judge by touch, but in the former by taste. For here again there is no discrepancy in the names used, in the case either of the original terms or of their contraries; for the contrary of sharp in either case is dull. [35]
Moreover, see if one use of a term has a contrary, while another has absolutely none; e.g. the pleasure of drinking has a contrary in the pain of thirst, whereas the pleasure of seeing that the diagonal is incommensurate with the side has none, so that pleasure is used in more than one way. To love also, used of the frame of mind, [106b1] has to hate as its contrary, while as used of the physical activity it has none; clearly, therefore, to love is homonymous.
Further, see in regard to their intermediates, if one use has an intermediate, while another has none, or if both have one but not the same one, as e.g. clear and [5] obscure in the case of colours have grey as an intermediate, whereas
in the case of sound they have none, or, if they have, it is muffled, as some people say that a muffled sound is intermediate. Clear, then, is homonymous, and likewise also obscure.
See, moreover, if some of them have more than one intermediate, while others have but one, as is the case with clear and obscure; for in the case of colours there [10] are numbers of intermediates, whereas in regard to sound there is but one, viz. muffled.
Again, in the case of the contradictory opposite, look and see if it is used in more than one way. For if it is, then the opposite of it also will be used in more than [15] one way; e.g. to fail to see is used in more than one way, viz. to fail to possess the power of sight, and to fail to put that power to active use. But if this is used in more than one way, it follows necessarily that to see also is used in more than one way; for there will be an opposite to each way of failing to see; e.g. the opposite of failing to possess the power of sight is to possess it, while of failing to put the power of sight to active use, the opposite is to put it to active use. [20]