by Aristotle
The rule based on things that are in a like relation differs from the rule based on attributes that belong in a like degree, because the former point is secured by [25] analogy, not from reflection on the belonging of any attribute, while the latter is judged by a comparison based on the fact that an attribute belongs.
9 · Next, for destructive purposes, see if in rendering the property potentially, he has also through that potentiality rendered the property relatively to something that does not exist, when the potentiality cannot belong to what does not [30] exist; for then what is stated to be a property will not be a property. Thus (e.g.) he who has said that breathable is a property of air has rendered the property potentially (for that is breathable which is such as can be breathed), and he has also rendered the property relatively to what does not exist (for while air may exist, even though there exists no animal so constituted as to breathe the air, it is not possible to [35] breathe it if no animal exists; so that it will not be a property of air to be such as can be breathed at a time when there exists no animal such as to breathe it) and so it follows that breathable will not be a property of air.
[139a1] For constructive purposes, see if in rendering the property potentially he renders the property either relatively to something that exists, or to something that does not exist, when the potentiality can belong to what exists;30 for then what has been stated not to be a property will be a property. Thus (e.g.) he who renders it as a [5] property of existing to be capable of being acted upon or of acting, in rendering the property potentially, has rendered the property relatively to something that exists; for when it is existent, it will be capable of being acted upon or of acting in a certain way; so that to be capable of being acted upon or of acting will be a property of existing.
Next, for destructive purposes, see if he has stated the property in the [10] superlative; for then what has been stated to be a property will not be a property. For people who render the property in that way find that of the object of which the account is true, the name is not true as well; for though the object perishes the account will continue in being none the less; for it will belong in the greatest degree to something that is in being. An example would be supposing anyone were to [15] render the lightest body as a property of fire; for, though fire may perish, there will still be some form of body that is the lightest, so that the lightest body will not be a property of fire. For constructive purposes, on the other hand, see if he has avoided rendering the property in the superlative; for then the property will in this respect have been correctly stated. Thus (e.g.) inasmuch as he who states a naturally civilized animal as a property of man has not rendered the property in the superlative, the property will in this respect have been correctly stated. [20]
BOOK VI
1 · The discussion of definitions falls into five parts. For you have to show either that it is not true at all to apply the account to that to which the name is [25] applied (for the definition of man ought to be true of every man); or that though the object has a genus, he has failed to put the object defined into the genus, or to put it into the appropriate genus (for the framer of a definition should first place the object in its genus, and then append its differences; for of the elements of the definition the genus seems to be the principal mark of the substance of what is defined); or that the account is not proper to the object (for, as we said above as [30] well,31 a definition ought to be proper); or else see if, though he has observed all the aforesaid cautions, he has yet failed to define the object, that is, to express the essence of what is being defined. It remains, apart from the foregoing, to see if he has defined it, but defined it incorrectly. [35]
Whether, then, the account is not also true of that of which the name is true you should examine according to the commonplace rules that relate to accident. For there too the question is always ‘Is so and so true or untrue?’; for whenever we argue [139b1] that an accident belongs, we declare it to be true, while whenever we argue that it does not belong, we declare it to be untrue. Whether he has failed to place the object in the appropriate genus, or whether the given account is not proper, we must examine according to the commonplace rules that relate to genus and property. [5]
It remains, then, to say how to investigate whether the object has been either not defined at all, or else defined incorrectly. First, then, we must examine if it has been defined incorrectly; for with anything it is easier to do it than to do it correctly—clearly, then, more mistakes are made in the latter task on account of its greater difficulty, so that the attack becomes easier in the latter case than in the [10] former.
Incorrectness falls into two branches: first, the use of obscure language (for the language of a definition ought to be the very clearest possible, seeing that the purpose of rendering it is to make something known); secondly, if the account is [15] longer than is necessary (for all additional matter in a definition is superfluous). Again, each of the aforesaid branches is divided into a number of others.
2 · One commonplace rule, then, in regard to obscurity is to see if what is stated is homonymous with something, e.g. that becoming is a passage into being, or [20] that health is the balance of hot and cold elements. Here passage and balance are homonymous; it is accordingly not clear which of the several possible senses of the term he intends to convey. Likewise also, if the term defined is used in different [25] ways and he has spoken without distinguishing between them; for then it is not clear to which of them the definition rendered applies, and one can then bring a captious objection on the ground that the account does not apply to all the things whose definition he has rendered—this kind of thing is particularly easy in the case where the definer does not see the homonymy. Or, again, the questioner may himself [30] distinguish the various uses of the term rendered in the definition, and then produce a deduction; for if the expression used is not adequate to the subject in any of its senses, it is clear that he cannot have defined it aright.
Another rule is to see if he has used a metaphorical expression, as, for instance, if he has defined knowledge as unsupplantable, or the earth as a nurse, or temperance as a harmony. For a metaphorical expression is always obscure. It is [35] possible, also, to argue captiously against the user of a metaphorical expression as though he had used it in its literal sense; for the definition stated will not apply, e.g. in the case of temperance; for harmony is always found between notes. Moreover, if harmony is the genus of temperance, then the same object will occur in two genera [140a1] of which neither contains the other; for harmony does not contain virtue, nor virtue harmony.
Again, see if he uses terms that are not in current use, as when Plato describes the eye as brow-shaded, or a certain spider as poison-fanged, or the marrow as [5] bone-formed. For an unusual phrase is always obscure.
Sometimes a phrase is used neither homonymously, nor yet metaphorically, nor yet literally, as when the law is said to be the measure or image of the things that are by nature just. Such phrases are worse than metaphor; for metaphor does make [10] what it signifies to some extent familiar because of the likeness involved (for those who use metaphors do so always in view of some likeness), whereas this kind of thing makes nothing familiar, (for there is no likeness in virtue of which the law is a measure or image nor is the law ordinarily so called). So then, if a man says that the law is literally a measure or an image, he speaks falsely; for an image is something [15] produced by imitation, and this is not found in the case of the law. If, on the other hand, he does not mean the term literally, it is clear that he has used an obscure expression, and one that is worse than any sort of metaphorical expression.
Moreover, see if from the expression used the account of the contrary is not clear; for definitions that have been correctly rendered also indicate their contraries [20] as well. Or, again, see if, when it is merely stated by itself, it is not evident what it defines—just as in the works of the old painters, unless there were an inscription, the figures used to be unrecognizable.
3 · I
f, then, the definition is not clear, you should examine on lines such as these. If he has phrased the definition redundantly, first of all look and see whether [25] he has used any attribute that belongs universally, either to entities in general, or to all that fall under the same genus as the object defined; for the mention of this is sure to be redundant. For the genus ought to divide the object from other things, and the differentia from any of the things contained in the same genus. Now any term that belongs to everything separates off the given object from absolutely nothing, while any that belongs to all the things that fall under the same genus does [30] not separate it off from the things contained in the same genus. Any addition, then, of that kind will be pointless.
Or see if, though the additional matter is proper to the given term, yet when it is struck out the rest of the account too is proper and makes clear the substance of the term. Thus, in the account of man, the addition ‘capable of receiving knowledge’ [35] is superfluous; for strike it out, and still the account is proper and makes clear his substance. Speaking generally, everything is superfluous upon whose removal the [140b1] remainder still makes the term that is being defined clear. Such, for instance, would also be the definition of the soul, assuming it to be stated as a self-moving number; for the soul is just what is self-moving, as Plato defined it.32 Or perhaps the expression used, though proper, yet does not show the substance if number is [5] eliminated. Which of the two is the real state of the case it is difficult to determine clearly: the right way to treat the matter in all cases is to be guided by convenience. Thus (e.g.) it is said that the definition of phlegm is the undigested moisture that comes first off food. What is first is one, not many; so that the addition of the word ‘undigested’ is superfluous; so that even when this is left out the remaining account [10] will still be proper; for it is impossible that both phlegm and also something else should both be the first to arise from the food. Or perhaps the phlegm is not absolutely the first thing to come off the food, but only the first of the undigested matters, so that the addition ‘undigested’ is required; for stated the other way the definition would not be true unless the phlegm comes first of all. [15]
Moreover, see if anything contained in the account fails to apply to everything that falls under the same species; for this sort of account is worse than those which include an attribute belonging to all things universally. For in that case, if the remainder of the account is proper, the whole too will be proper; for absolutely always, if to something proper anything whatever that is true is added, the whole too [20] becomes proper. Whereas if any part of the account does not apply to everything that falls under the same species, it is impossible that the account as a whole should be proper; for it will not be predicated convertibly with the object; e.g. a terrestrial two-footed animal six feet high—for an account of that kind is not predicated convertibly with the object, because being six feet high does not belong to [25] everything that falls under the same species.
Again, see if he has said the same thing more than once, saying (e.g.) that desire is appetition for the pleasant. For desire is always for the pleasant, so that what is the same as desire will also be for the pleasant. Accordingly our definition of desire becomes appetition for the pleasant for the pleasant; for there is no difference [30] between desire and appetition for the pleasant, so that both alike will be for the pleasant. Or perhaps there is no absurdity in this; for man is a biped; therefore, what is the same as man is a biped; but a terrestrial biped animal is the same as man, and [35] therefore a terrestrial biped animal is a biped. But this involves no real absurdity. For biped is not predicated of terrestrial animal (if it were, then we should certainly have biped predicated twice of the same thing); but the subject said to be a biped is [141a1] a terrestrial biped animal, so that biped is only predicated once. Likewise in the case of desire as well; for being of the pleasant is not predicated of appetition, but rather of the whole, so that there too the predication is only made once. Absurdity results, [5] not when the same word is uttered twice, but when the same thing is more than once predicated of a subject—as Xenocrates says that prudence defines and contemplates reality; for definition is a certain type of contemplation, so that by adding ‘and contemplates’ he says the same thing twice over. Likewise those who say that [10] cooling is the privation of natural heat. For all privation is a privation of some natural attribute, so that the addition of ‘natural’ is superfluous: it would have been enough to say privation of heat, for privation itself makes it familiar that the heat meant is natural heat.
[15] Again, see if a universal has been mentioned and then a particular case of it added as well, e.g. Equity is a remission of what is expedient and just; for what is just is a branch of what is expedient and is therefore included in the latter: it is therefore redundant, an addition of the particular after the universal has been already stated. So also, if he defines medicine as knowledge of what makes for [20] health in animals and men, or the law as the image of what is by nature noble and just; for what is just is a branch of what is noble, so that he says the same thing more than once.
4 · Whether, then, a man defines a thing correctly or incorrectly you should examine on these and similar lines. But whether he has mentioned and defined its [25] essence or not, should be examined as follows.
First of all, see if he has failed to make the definition through terms that are prior and more familiar. For a definition is rendered in order to come to know the term stated, and we come to know things by taking not any random terms, but such [30] as are prior and more familiar, as is done in demonstrations (for so it is with all teaching and learning); accordingly, it is clear that a man who does not define through terms of this kind has not defined at all. Otherwise, there will be more than one definition of the same thing; for clearly he who defines through terms that are prior and more familiar has framed a better definition, so that both will then be definitions of the same object. This sort of thing, however, does not seem to be so; for [35] of each entity there is a single essence; if, then, there are to be a number of definitions of the same thing, the object defined will be the same as the essences represented in each of the definitions; but these are not the same, inasmuch as the [141b1] definitions are different. Clearly, then, any one who has not defined a thing through terms that are prior and more familiar has not defined it at all.
The statement that a definition has not been made through more familiar terms may be understood in two ways either supposing that its terms are without qualification less intelligible, or supposing that they are less intelligible to us; for [5] either way is possible. Thus the prior without qualification is more familiar than the posterior, a point, for instance, than a line, a line than a plane, and a plane than a solid; just as a unit is more intelligible than a number; for it is prior to and a principle of all number. Likewise, also, a letter is more familiar than a syllable. Whereas to us it sometimes happens that the converse is the case; for a solid falls under perception most of all, and a plane more than a line, and a line more than a [10] point; for most people learn such things earlier; for any ordinary intelligence can grasp them, whereas the others require a precise and exceptional understanding.
Absolutely, then, it is better to try to come to know what is posterior through [15] what is prior, inasmuch as such a way of procedure is more scientific. Of course, in dealing with persons who cannot recognize things through terms of that kind, it may perhaps be necessary to frame the account through terms that are familiar to them. Among definitions of this kind are those of a point, a line, and a plane, all of which [20] explain the prior by the posterior; for they say that a point is the limit of a line, a line of a plane, a plane of a solid. One must, however, not fail to observe that those who define in this way cannot show the essence of what they define, unless it so happens that the same thing is more familiar both to us and also without qualification, since [25] a correct definition must define a thing through its genus and its differentiae, and these belong to the order o
f things which are without qualification more familiar than, and prior to, the species. For annul the genus and differentia, and the species too is annulled, so that these are prior to the species. They are also more familiar; for if the species is known, the genus and differentia must of necessity be known as [30] well (for any one who knows what a man is knows also what animal and terrestrial are), whereas if the genus or the differentia is known it does not follow of necessity that the species is known as well; thus the species is less intelligible. Moreover, those who say that such definitions, viz. those which proceed from what is familiar to [35] some individual, accord with the truth, will have to say that there are several definitions of one and the same thing. For in fact different things are more familiar to different people, not the same things to all; and so a different definition would have to be rendered to each several person, if the definition is to be constructed from [142a1] what is more familiar to particular individuals. Moreover, to the same people different things are more familiar at different times: first of all the objects of sense; then, as they become more acute, the converse; so that those who hold that a definition ought to be rendered through what is more familiar to particular individuals will not have to render the same definition at all times even to the same [5] person. It is clear, then, that the right way to define is not through terms of that kind, but through what is without qualification more familiar; for only in this way could the definition come always to be one and the same. Perhaps, also, what is familiar without qualification is what is familiar, not to all, but to those who are in a [10] sound state of understanding, just as what is without qualification healthy is what is healthy to those in a sound state of body. All such points as this ought to be made very precise, and made use of in the course of discussion as occasion requires.