by Aristotle
Moreover, examine the case of terms that are opposed as privation and possession; for if the one term is used in more than one way, then so will the remaining term: e.g. if to perceive is used in more than one way, as applied to the soul and to the body, then to be imperceptive too will be used in more than one way, as applied to the soul and to the body. That the opposition between the terms now in [25] question depends upon privation and possession is clear, since animals naturally possess each kind of perception, both as applied to the soul and as applied to the body.
Moreover, examine the inflected forms. For if ‘justly’ is used in more than one way, the ‘just’, also, will be used in more than one way; for there will be a ‘just’ [30] corresponding to each ‘justly’; e.g. if ‘justly’ is used of judging according to one’s own opinion, and also of judging as one ought, then ‘just’ also will be used in like manner. In the same way also, if ‘healthy’ is used in more than one way, then [35] ‘healthily’ also will be used in more than one way: e.g. if healthy is what produces health and what preserves health and what betokens health, then ‘healthily’ also will be used to mean ‘in such a way as to produce’ or ‘preserve’ or ‘betoken’ health. Likewise also in other cases, whenever the original term is used in more than one [107a1] way, the inflexion also that is formed from it will be used in more than one way, and vice versa.
Look also at the classes of the predicates signified by the term, and see if they are the same in all cases. For if they are not the same, then clearly the term is [5] homonymous: e.g. good in the case of food is what is productive of pleasure, and in the case of medicine what is productive of health, whereas as applied to the soul it is to be of a certain quality, e.g. temperate or courageous or just; and likewise also, as applied to a man. Sometimes it signifies what happens at a certain time, as (e.g.) what happens at the right time; for what happens at the right time is called good. [10] Often it signifies what is of a certain quantity, e.g. as applied to the proper amount; for the proper amount too is called good. So then good is homonymous. In the same way also clear, as applied to a body, signifies a colour, but in regard to a sound it denotes what is easy to hear. Sharp, too, is in a closely similar case; for the same [15] term does not have the same use in all its applications; for a sharp note is a swift note, as the mathematical theorists of harmony tell us, whereas a sharp angle is one that is less than a right angle, while a sharp dagger is one cut at a sharp angle.
Look also at the genera of the objects denoted by the same name, and see if they are different without the one falling under the other, as (e.g.) donkey is both [20] the animal and the engine. For the account of them that corresponds to the name is different; for the one will be declared to be an animal of a certain kind, and the other to be an engine of a certain kind. If, however, the genera are subordinate one to the other, there is no necessity for the accounts to be different. Thus (e.g.) animal is the genus of raven, and so is bird. Whenever therefore we say that the raven is a bird, we [25] also say that it is a certain kind of animal, so that both the genera are predicated of it. Likewise also whenever we call the raven a winged two-footed animal, we declare it to be a bird; in this way, then, as well, both the genera are predicated of raven. But in the case of genera that are not subordinate one to the other this does not happen; [30] for whenever we call a thing an engine, we do not call it an animal, nor vice versa.
Look also and see not only if the genera of the term before you are different without being subordinate one to the other, but also in the case of its contrary; for if [35] its contrary is used in many ways, clearly the term before you is as well.
It is useful also to look at the definition that arises from the use of the term in combination, e.g. of a clear body and of a clear sound. For then if what is proper to each case be abstracted, the same phrase ought to remain over. This does not happen in the case of homonyms, e.g. in the cases just mentioned. For the former [107b1] will be a body possessing such and such a colour, while the latter will be a sound easy to hear. Abstract, then, ‘a body’ and ‘a sound’, and the remainder in each case is not the same. It should, however, have been, had clear in each case been [5] synonymous.
Often in the actual accounts as well homonymy creeps in without being noticed, and for this reason the accounts also should be examined. If (e.g.) any one describes what betokens and produces health as being in a balanced state, we must not desist but go on to examine in what sense he has used the term ‘balanced’ in each [10] case, e.g. if in the latter case it means that it is of the right amount to produce health, whereas in the former it means that it is such as to betoken what kind of state prevails.
Moreover, see if the terms cannot be compared as more or less or as in like degree, as is the case (e.g.) with a clear sound and a clear argument,5 and a sharp flavour and a sharp sound. For neither are these things said to be clear or sharp in a [15] like degree, nor yet is the one said to be clearer or sharper than the other. Clear, then, and sharp are homonymous. For synonyms are always comparable; for they will always hold either in like manner, or else in a greater degree in one case.
Now since of genera that are different without being subordinate one to the other the differentiae also are different in kind, e.g. those of animal and knowledge [20] (for the differentiae of these are different), look and see if the items falling under the same term are differentiae of genera that are different without being subordinate one to the other, as e.g. sharp is of a sound and a body. For being sharp differentiates sound from sound, and likewise also one body from another. Sharp, then, is homonymous; for it forms differentiae of genera that are different without [25] being subordinate one to the other.
Again, see if the items falling under the same term themselves have different differentiae, e.g. colour in bodies and colour in tunes; for the differentiae of colour in bodies are dispersing the eye and compressing the eye, whereas colour in melodies [30] has not the same differentiae. Colour, then, is homonymous; for things that are the same have the same differentiae.
Moreover, since the species is never the differentia of anything, look and see if one of the items falling under the same term is a species and another a differentia, as (e.g.) clear as applied to a body is a species of colour, whereas in the case of a [35] sound it is a differentia; for one sound is differentiated from another by being clear.
16 · Thus when a term is used in many ways, it may be investigated by these and like means. The differences which things present to each other should be [108a1] examined both in the genera themselves (e.g. ‘Wherein does justice differ from courage, and wisdom from temperance?’—for all these belong to the same genus); and also from one genus to another, provided they are not too far apart (e.g. ‘Wherein does perception differ from knowledge?’); for in the case of genera that [5] are very far apart, the differences are entirely obvious.
17 · Likeness should be studied, first, in the case of things belonging to different genera, the formula being: as one is to one thing, so is another to another (e.g. as knowledge stands to the object of knowledge, so is perception related to the [10] object of perception), or: as one is in one thing, so is another in another (e.g. as sight is in the eye, so is intellect in the soul, and as is a calm in the sea, so is windlessness in the air). Practice is more especially needed in regard to terms that are far apart; for in the case of the rest, we shall be more easily able to see the points of likeness. We should also look at things which belong to the same genus, to see if any identical [15] attribute belongs to them all, e.g. to a man and a horse and a dog; for in so far as they have any identical attribute, in so far they are alike.
18 · It is useful to have examined the number of uses of a term both for clearness’ sake (for a man is more likely to know what it is he asserts, if it has been [20] made clear to him how many uses it may have), and also with a view to ensuring that our deductions shall be in accordance with the actual facts and not addressed merely to the word used. For as long as it is not clear in how many
ways a term is used, it is possible that the answerer and the questioner are not directing their minds upon the same thing; whereas when once it has been made clear how many uses there are, and also upon which of them the former directs his mind when he makes [25] his assertion, the questioner would then look ridiculous if he failed to address his argument to this. It helps us also both to avoid being misled and to mislead by fallacies; for if we know the number of uses of a term, we shall certainly never be misled by fallacy, but shall know if the questioner fails to address his argument to the same point; and when we ourselves put the questions we shall be able to mislead [30] him, if our answerer happens not to know the number of uses of our terms. This, however, is not possible in all cases, but only when of the many uses some are true and others are false. This manner of argument, however, does not belong properly to dialectic; dialecticians should therefore by all means beware of this kind of verbal [35] discussion, unless any one is absolutely unable to discuss the subject before him in any other way.
The discovery of differences helps us both in deductions about sameness and difference, and also in recognizing what any particular thing is. That it helps us in [108b1] deductions about sameness and difference is clear; for when we have discovered a difference of any kind whatever between the objects before us, we shall already have proved that they are not the same; while it helps us in recognizing what a thing is, [5] because we usually distinguish the account that is proper to the substance of each particular thing by means of the differentiae that are appropriate to it.
The examination of likeness is useful with a view both to inductive arguments and to hypothetical deductions, and also with a view to the rendering of definitions. [10] It is useful for inductive arguments, because it is by means of an induction of particulars in cases that are alike that we claim to induce the universal; for it is not easy to do this if we do not know the points of likeness. It is useful for hypothetical deductions because it is a reputable opinion that among similars what is true of one is true also of the rest. If, then, with regard to any of them we are well supplied with [15] matter for a discussion, we shall secure a preliminary admission that however it is in these cases, so it is also in the case before us; then when we have proved the former we shall have proved, on the strength of the hypothesis, the matter before us as well; for we have first made the hypothesis that however it is in these cases, so it is also in the case before us, and have then produced the demonstration. It is useful for the rendering of definitions because, if we are able to see what is the same in each [20] individual case of it, we shall be at no loss when we define it; for of the common predicates that which is most definitely predicated in what the thing is is likely to be the genus. Likewise, also, in the case of objects widely divergent, the examination of likeness is useful for purposes of definition, e.g. the sameness of a calm at sea, and [25] windlessness in the air (each being a form of rest), and of a point on a line and the unit in number (each being a principle). If, then, we render as the genus what is common to all the cases, we shall get the credit of defining not inappropriately. Definition-mongers too nearly always render them in this way; for they declare the unit to be the principle of number, and the point the principle of a line. It is clear, [30] then, that they place them in that which is common to both as their genus.
The instruments, then, whereby deductions are effected, are these; the commonplace rules, for the observance of which the aforesaid instruments are useful, are as follows.
BOOK II
1 · Of problems some are universal, others particular. Universal problems are such as ‘Every pleasure is good’ and ‘No pleasure is good’; particular problems [35] are such as ‘Some pleasure is good’ and ‘Some pleasure is not good.’ The methods of establishing and overthrowing a view universally are common to both kinds of [109a1] problems; for when we have proved that a predicate belongs in every case, we shall also have proved that it belongs in some cases. Likewise, also, if we prove that it does [5] not belong in any case, we shall also have proved that it does not belong in every case. First, then, we must speak of the methods of overthrowing a view universally, because such are common to both universal and particular problems, and because people more usually introduce theses asserting a predicate than denying it, while those who argue with them overthrow it.
The conversion of an appropriate name which is derived from an accident is an extremely precarious thing; for in the case of accidents and in no other it is possible [10] for something to be true in a certain respect and not universally. Names derived from definition and property and genus are bound to be convertible; e.g. if being a two-footed terrestrial animal belongs to something, then it will be true by conversion to say that it is a two-footed terrestrial animal. Likewise, also, if derived [15] from the genus; for if being an animal belongs to something, then it is an animal. The same is true also in the case of a property; for if being capable of learning grammar belongs to something, then it will be capable of learning grammar. For none of these attributes can possibly belong or not belong in part; they must either belong or not belong absolutely. In the case of accidents, on the other hand, there is [20] nothing to prevent an attribute (e.g. whiteness or justice) belonging in part, so that it is not enough to show that whiteness or justice belongs to a man in order to show [25] that he is white or just; for it is open to dispute it and say that he is white or just in part only. Conversion, then, is not a necessary process in the case of accidents.
We must also define the errors that occur in problems. They are of two kinds, caused either by false statement or by transgression of the established use of language. For those who make false statements, and say that something belongs to a [30] thing which does not belong to it, commit error; and those who call objects by the names of other objects (e.g. calling a plane-tree a man) transgress the established terminology.
2 · Now one commonplace rule is to look and see if a man has ascribed as an [35] accident what belongs in some other way. This mistake is most commonly made in regard to the genera of things, e.g. if one were to say that being a colour is an accident of white—for being a colour does not happen by accident to white, but colour is its genus. The assertor may of course make the mistake in so many words, [109b1] saying (e.g.) that it is an accident of justice to be a virtue; but often even without such explicitness it is obvious that he has rendered the genus as an accident; e.g. suppose that one were to say that whiteness is coloured or that walking is in motion. For a predicate drawn from the genus is never ascribed to the species in a derived [5] form, but always the genera are predicated of their species synonymously; for the species take on both the name and the account of their genera. A man therefore who says that white is coloured has not rendered it as its genus, seeing that he has used a derived form, nor yet as its property or as its definition; for the definition and [10] property of a thing belong to it and to nothing else, whereas many things besides white are coloured, e.g. a log, a stone, a man, a horse. Clearly then he renders it as an accident.
Another rule is to examine all cases where a predicate has been said to belong to all or none of something. Look at them species by species, and not in their infinite [15] multitude; for then the inquiry will proceed more directly and in fewer steps. You should look and begin with the primitives, and then proceed in order down to those that are not further divisible: e.g. if a man has said that the knowledge of opposites is the same, you should look and see whether it be so of relative opposites and of contraries and of terms opposed as privation and possession, and of contradictory [20] terms. Then, if no clear result is reached so far in these cases, you should again divide these until you come to those that are not further divisible, and see (e.g.) whether it is so of just deeds and unjust, or of the double and the half, or of blindness and sight, or of being and not-being; for if in any case it is proved that the knowledge of them is not the same we shall have demolished the problem. Likewise, also, if the [25] predicate belongs in no case. This rule is convertible fo
r both destructive and constructive purposes; for if, as we proceed with the division, the predicate appears to hold in all or in a large number of cases, we may then claim that the other should actually assert it universally, or else bring an objection to show in what case it is not so; for if he does neither of these things, a refusal to assert it will make him look absurd.
[30] Another rule is to make accounts both of an accident and of its subject, either of both separately or else of one of them, and then look and see if anything untrue has been assumed as true in the accounts. Thus (e.g) to see if it is possible to wrong a god, ask what is to wrong? For if it be to injure deliberately, clearly it is not possible for a god to be wronged; for it is impossible that God should be injured. Again, to see if the good man is jealous, ask who is the jealous man and what is jealousy. For if [35] jealousy is pain at the apparent success of some honest person, clearly the good man is not jealous; for then he would be bad. Again, to see if the indignant man is jealous, ask who each of them is; for then it will be obvious whether the statement is true or false; e.g. if he is jealous who grieves at the successes of the good, and he is indignant [110a1] who grieves at the successes of the evil, then clearly the indignant man would not be jealous. A man should substitute accounts also for the words contained in his [5] account, and not stop until he comes to something familiar; for often when the account is given as a whole, the point at issue is not cleared up, whereas if for one of the words used in the account an account be stated, it becomes obvious.