Authors/Thomas Aquinas/posteriorum/L2/Lect14

Lecture 14 Dividing the genus to investigate which items should be put in a definition

Latin	English
	Lecture 14 (96b15-97a6) DIVIDING THE GENUS TO INVESTIGATE WHICH ITEMS SHOULD BE PUT IN A DEFINITION
lib. 2 l. 14 n. 1 Postquam philosophus ostendit qualia oportet esse ea quae constituunt definitionem significantem essentiam rei, hic ostendit qualiter debeant investigari. Et circa hoc duo facit: primo, proponit modum maxime convenientem ad investigandum ea quae sunt in definitione ponenda, scilicet per divisionem generis; secundo, ponit quemdam alium modum per similia et differentia; ibi: quaerere autem oportet et cetera. Circa primum duo facit: primo, ostendit quod oportet uti divisione generis ad investigandum particulas definitionis; secundo, ostendit quid oporteat in tali investigatione observari; ibi: ad consequendum autem terminum et cetera. Circa primum duo facit: primo, ostendit veritatem; secundo, excludit errorem; ibi: nihil autem oportet dividentem et cetera. Circa primum tria facit: primo, ostendit qualiter per divisionem generis investigentur definitionis particulae; secundo, quomodo processus divisionis sit utilis ad propositum; ibi: divisiones autem quae sunt etc.; tertio, quomodo sunt cavenda ea, quae circa hunc processum defectum inducere possunt; ibi: differt autem et cetera. Circa primum duo facit: primo, ostendit quod oportet uti divisione generis ad definiendum; secundo, quomodo oportet accipere differentias; ibi: post autem accepto et cetera.	After showing what should be the characteristics of the items which constitute the definition signifying the essence of a thing, the Philosopher now shows how they should be investigated. Concerning this he does two things. First, he proposes the most suitable method of investigating the items to be put in the definition, namely, by division of the genus. Secondly, he sets forth another method, namely, by similarities and differences (97b7) [L. 16]. Concerning the first he does two things. First, he shows that one should employ division of the genus for investigating the particles of the definition. Secondly, he shows what to look for in such an investigation (97a23) [L. 15]. In regard to the first he does two things. First, he shows the truth. Secondly, he excludes an error (97a6) [L. 151. Concerning the first he does three things. First, he shows how the particles of a definition are investigated by the method of dividing the genus. Secondly, how the process of division is useful for this task (96b25). Thirdly, how to avoid pitfalls which can invalidate this process (96b30). Concerning the first he does two things. First, he shows that one should employ division of the genus for defining. Secondly, how one should take the differences (96b18).
lib. 2 l. 14 n. 2 Dicit ergo primo quod cum aliquis vult negotiari, ad definiendum, aliquod totum, idest universale, congruum est ut primo dividat genus in primas partes illius generis, quae sunt indivisibiles secundum speciem, puta quod dividat numerum in binarium et ternarium: et hac divisione praemissa, per quam cognoscitur genus, tentet postea accipere definitionem singularum specierum; sicut etiam fit in aliis, puta in recta linea et in circulo et in recto angulo. Omnia enim haec congrue definiuntur, praemissa divisione generis.	He says therefore first (96b15) that when someone wishes to deal with some whole, i.e., a universal, in order to define it, it is recommended that he first divide the genus into the first parts of that genus, i.e., those that are not further divisible into species; for example, he should divide number into two and three. Having accomplished this division through which the genus is known, he should then try to obtain the definition of each species as is done in other matters, say in the matter of straight line and circle and right angle. For all these are fittingly defined after one has divided the genus.
lib. 2 l. 14 n. 3 Deinde cum dicit: post haec autem accipientem etc., ostendit qualiter sint accipiendae differentiae; et dicit quod postquam acceperimus per divisionem generis in species quid sit genus, puta utrum sit in genere qualitatis vel quantitatis, oportet ad investigandum differentias considerare proprias passiones, quae, sicut dictum est, sunt signa manifestantia formas proprias specierum. Et hoc oportet primum facere per aliqua communia. Si enim nos congregemus accidentia ex generibus communioribus (quae hic dicuntur indivisibilia, quia non resolvuntur in aliqua priora genera), statim ex definitionibus eorum erunt manifesta ea quae quaerimus. Oportet enim omnium definitionum esse principium id quod simplex est, idest genus commune: et huiusmodi simplicibus solum per se insunt accidentia, quae communiter inveniuntur in multis; omnibus autem aliis conveniunt secundum illa. Sicut album et nigrum per se quidem conveniunt corpori terminato, et secundum hoc commune conveniunt et homini et equo et quibuscunque aliis. Unde si oporteret accipere definitionem alicuius, cui universaliter conveniret album, puta definitionem nivis, oporteret recurrere ad genus communius, quod est corpus terminatum, et ex eo investigare causam albedinis; et secundum hoc ostenderetur nobis quare nix universaliter sit alba. Et illa causa poterit pertinere ad quod quid est nivis; puta inspissatio humidi, quae facit humidum terminari cum conservatione lucis.	Then (96b18) he shows how to obtain the differences, saying that after we have learned what the genus is by dividing the genus into its species, for example, whether it is in the genus of quality or quantity, the next step is to investigate the differences by considering the proper attributes which, as has been said, are signs manifesting the forms proper to the species. And this should first be done by means of certain common items. For if we assemble the accidents from the more common genera (which he here calls indivisibles, because they are not resolved into prior genera), then from their definitions the things we are searching for will be immediately obvious. For “the basic element of all definitions must be something simple,” i.e., a common genus; furthermore, it is only in such simple things that the accidents inhere per se which are commonly found in many, but they are found in all other things in virtue of those simple genera. For example, black and white belong per se to terminated body; and in virtue of this common characteristic they belong also to man and horse and other things. Hence if one is to obtain the definition of something to which white belongs universally, say the definition of snow, he must have recourse to the more common genus, such as terminated body, and obtain from it the cause of whiteness; and according to this we would learn why snow is white universally. And that cause could pertain to the quod quid of snow: for example, the solidifying of a moist element which makes it be terminated, some light being preserved.
lib. 2 l. 14 n. 4 Deinde cum dicit: divisiones autem quae sunt etc., ostendit quomodo praedictus processus conferat ad definitiones; et dicit quod ad hoc quod aliquis praedicto modo procedat ad definiendum, scilicet dividendo genus in species, utile est quod homo accipiat divisionem generis per differentias. Sed tamen quomodo per hoc manifestetur quod quid est, dictum est in praecedentibus. Sunt quidem utiles praedictae divisiones ad accipiendum quod quid est sic solum, sicut dictum est; sed ad syllogizandum quod quid est nihil videntur facere, ut prius dictum est. Sed videtur quod dividentes statim accipiant omnia non syllogizata, sicut si a principio aliquis accepisset, antequam divideret.	Then (96b25) he shows how the above method is useful in definitions. And he says that when someone seeks to define according to the above method, i.e., by dividing the genus into species, the benefit it confers is that it accomplishes the division of the genus through differences. How this method reveals the quod quid has been indicated above. Furthermore, these divisions are useful for achieving the quod quid solely in the manner described above; they seem to contribute nothing to the syllogizing of the quod quid, as we said earlier. Rather it seems that upon dividing, one immediately obtains everything without syllogizing, as though he knew them from the beginning before he divided.
lib. 2 l. 14 n. 5 Deinde cum dicit: differt autem aliquid prius etc., ostendit quid oporteat cavere, ne circa praedictum processum defectus accidat. Et circa hoc duo facit: primo, ostendit quod oportet cavere inordinationem: secundo, quod oportet cavere diminutionem; ibi: amplius autem ad nil relinquendum et cetera. Dicit ergo primo quod multum differt quid prius et quid posterius praedicetur inter ea quae ponuntur in definitione. Potest enim uno modo sic dici, quod homo est animal mansuetum bipes; alio modo potest aliter ordinari, ut dicatur quod homo est bipes animal mansuetum. Et quod hoc differat ad definiendum patet per hoc, quod oportet omne quod definitur constitui ex duobus, scilicet ex genere et differentia. Sic igitur si mansuetum accipitur ut differentia animalis, oportet quod animal mansuetum sit aliquid unum quod accipiatur ut genus, ex quo et alia differentia quae est bipes, constituatur homo. Et eadem ratio est de quocunque alio quod fit unum ex pluribus per se, et non per accidens.	Then (96b30) he shows what to avoid if this method is not to fail. Concerning this he does two things. First, he shows that one must avoid improper order. Secondly, one must avoid diminution (96b35). He says therefore first (96b30) that it makes a great difference, when arranging the items present in a definition, which items are mentioned first and which are mentioned later. For it is possible to state that man is a gentle animal which is two-legged, or to state that man is a two-legged animal which is gentle. That the order of terms does make a difference in defining is clear from the fact that anything which is defined should be composed of two things, namely, a genus and a difference. Therefore, if “gentle” is taken as a difference of animal, it is required that “gentle animal” be some one thing which can be taken as a genus from which, with the addition of the difference “two-legged,” man is constituted. And the same reason holds for anything else which is formed from several things into a unit which is per se and not per accidens.
Sicut igitur differt quod accipiatur hoc vel illud pro genere vel differentia, aut quod accipiatur aliquid ut est differentia constitutiva generis et divisiva eiusdem; ita differt ad definiendum quod sic vel aliter partes definitionis ordinentur. Si enim dicam quod homo est animal mansuetum bipes, accipietur animal ut genus, mansuetum autem ut differentia constitutiva eius, bipes autem ut differentia divisiva ipsius. E converso autem erit si dicatur quod homo est animal bipes mansuetum. Quia igitur differentia ordinis facit differentiam in quod quid est, consequens est quod ille qui dividit, non solum supponat ea quae accipiuntur ad definiendum, sed etiam petat ordinem eorumdem. Et sic manifestum est quod definitio non syllogizat quod quid est.	Therefore, just as it does make a difference whether this or that be taken for the genus or the difference, or whether something is taken as a difference constituting the genus or as dividing it, so it makes a difference in defining just how the parts of the definition are ordered. For if I say that man is a two-legged gentle animal, “animal” will be taken as the genus, “gentle” as the difference constituting a genus, and “two-legged” as the difference dividing it. It will be the opposite if I say that man is a gentle two-legged animal. Therefore, since a variation in order makes a difference in quod quid, the consequence is that one who divides should not only suppose the things which are taken for defining, but should take care about the ordering of those things. And so it is clear that a definition does not syllogize the quod quid.
lib. 2 l. 14 n. 6 Deinde cum dicit: amplius autem ad nil relinquendum etc., docet cavere diminutionem, ostendens quomodo fieri possit ut nil praetermittatur eorum quae requiruntur ad quod quid est; et dicit quod hoc contingit fieri solum isto modo quo dicetur. Ad cuius evidentiam considerandum est, quod omnes differentiae superiorum generum pertinent ad quod quid est alicuius speciei. Nam inferius genus constituitur per differentiam divisivam superioris generis. Ad vitandum ergo diminutionem, oportet quod nulla huiusmodi differentiarum praetermittatur. Praetermittitur autem si aliquis, accepto supremo genere, accipiat consequenter aliquam differentiam divisivam non quidem ipsius supremi generis, sed alicuius inferioris. Quod quidem hoc modo cognosci potest: quia cum animal accipiatur aliquod supremum genus, si postea aliquis accipiat divisionem alicuius de inferioribus generibus, non totum quod continetur sub genere superiori cadet sub illa divisione.	Then (96b35) he teaches that one should avoid diminution, pointing out how to make certain that nothing required for the quod quid be omitted. And he says that the only way this can be avoided is by following the method he will indicate. To understand this it should be noted that all the differences of higher genera pertain to the quod quid of some species. For the lower genus is constituted by the difference which divides the higher genus. Therefore, to avoid diminution it is necessary that none of these differences be overlooked. But they are overlooked if someone, after taking the supreme genus, were to take a difference which divides not that supreme genus but some lower genus. But this can be recognized in the following way: when animal is taken as a supreme genus, if someone then takes the division of something pertaining to lower genera, not everything which is contained under the higher genus will fall into that division.
Et ponit ad hoc exemplum: sicut non omne animal est vel totalum, vel divisum pennis. Dicitur autem animal totalum, quod habet totas alas integras et continuas, sicut vespertilio; divisum autem pennis dicitur animal, cuius alae distinguuntur per diversas pennas, sicut accipitris vel corvi. Animali autem non habenti alas neutrum horum convenit; sed omne animal volatile continetur sub altera harum differentiarum, quia secundum praedictas differentias dividitur hoc genus quod est animal volatile. Sed prima et immediata differentia animalis attenditur ex hoc quod omne animal cadit sub divisione. Et ita est etiam de omnibus aliis generibus, sive accipiamus genera quae sunt extrinseca ab animali, sicut lapis et planta, sive illa quae sub animali continentur, sicut avis et piscis. Prima tamen differentia avis attenditur secundum differentiam in quam incidit omnis avis: et eadem ratio est de pisce.	As an example of this he says: for example, not every animal is either whole-winged or possessed of divided wings. (An animal is said to be whole-winged if its wings are each a continuous whole, as in a bat; but an animal is said to be possessed of divided wings if its wings are composed of distinct feathers, as in a hawk or raven). But neither of these belongs to a non-winged animal. However, any animal that flies is contained under one or other of these differences, because it is according to the above differences that this genus, flying animal, is divided. But the first and immediate difference of animal is such that every animal falls under the division. And the same applies to all other genera, whether we are dealing with genera extrinsic to animal, such as stone and plant, or those which are contained under animal, such as bird and fish. Yet the first difference of bird is such that every bird is included; and the same is true of fish.
Concludit ergo quod si aliquis sic procedat in dividendo, quod scilicet totum divisum contineatur sub partibus divisionis, poterit homo cognoscere quod nil est relictum de his quae sunt necessaria ad definiendum. Si autem aliter procedatur, necesse est quod aliqua relinquantur, et quod homo non cognoscat se integraliter definisse.	He concludes, therefore, that if someone proceeds to divide according to this method, namely, that the totality which is divided is contained under the parts of the division, he will be able to know that nothing necessary for defining has been omitted. But if he proceeds some other way, he is bound to omit something; and he will not be sure that he has defined integrally.