Authors/Thomas Aquinas/posteriorum/L2/Lect6

Lecture 6 Whether quod quid can be shown by demonstration or definition

Latin	English
	Lecture 6 (92b3-39) WHETHER QUOD QUID CAN BE SHOWN BY DEMONSTRATION OR DEFINITION
lib. 2 l. 6 n. 1 Postquam philosophus ostendit quod non contingit demonstrare quod quid est, inducendo per singulos modos quibus aliquid demonstrari potest, hic ostendit propositum per rationes communes. Et circa hoc tria facit: primo, praemittit quoddam quod est necessarium ad propositum ostendendum; secundo, ostendit propositum; ibi: at vero si demonstrabit quod quid est etc.; tertio, epilogat quae dicta sunt; ibi: ex his igitur neque definitio et cetera.	After considering each of the ways in which something might be demonstrated and showing that none can demonstrate the quod quid, the Philosopher now shows what he proposes through common reasons. Concerning this he does three things. First, he lays down something which is necessary for proving what he proposes. Secondly, he shows what he proposes (957). Thirdly, he sums up what has been stated (97b35).
lib. 2 l. 6 n. 2 Dicit ergo primo quod non videtur esse possibilis aliquis modus, quo aliquis demonstret quod quid est esse hominis; et hoc ideo, quia necesse est quod quicunque scit quod quid est esse hominis, vel cuiuscunque alterius rei, quod sciat rem illam esse. Quia enim non entis non est aliqua quidditas vel essentia, de eo quod non est, nullus potest scire quod quid est; sed potest scire significationem nominis, vel rationem ex pluribus nominibus compositam: sicut potest aliquis scire quid significat hoc nomen Tragelaphus vel Hircocervus, quod idem est, quia significat quoddam animal compositum ex hirco et cervo; sed impossibile est scire quod quid est Hircocervi, quia nihil est tale in rerum natura.	He says therefore first (92b3) that there does not seem to be any possible way for a person to demonstrate that some quod quid is man: and this because whoever knows a quod quid to be of man or of any other thing is required to know that the thing exists. For since there is no quiddity or essence of a non-being, it is impossible to know the quod quid of something which is not; but one might know the meaning of the name or have a notion composed of several names. Thus a person is capable of knowing the ‘ meaning of the word tragelaphus or goat-stag, because it signifies an animal composed of goat and stag, but it is impossible to know the quod quid of a goat-stag, because there is no such thing given in nature.
lib. 2 l. 6 n. 3 Deinde cum dicit: at vero si demonstrabit quid est etc., ex eo quod praemissum est, procedit ad propositum ostendendum. Et circa hoc duo facit: primo, ostendit quod non potest ostendi quod quid est demonstratione; secundo, quod non potest ostendi definitione; ibi: si ergo et definiens demonstrat et cetera. Circa primum ponit tres rationes; quarum prima talis est. Sicut definitio inducitur ad manifestandum aliquid unum, in quantum scilicet ex partibus definitionis fit unum per se, non per accidens, ita etiam oportet quod demonstratio, quae utitur definitione tanquam medio, unum aliquid demonstret: oportet enim conclusionem esse medio proportionatam. Et ita patet quod per unam et eamdem demonstrationem non possunt diversa demonstrari. Sed aliud est quod quid est homo, et esse hominem: in solo enim primo essendi principio, quod est essentialiter ens, ipsum esse et quidditas eius est unum et idem; in omnibus autem aliis, quae sunt entia per participationem, oportet quod sit aliud esse et quidditas entis. Non est ergo possibile quod eadem demonstratione demonstret aliquis quid est et quia est.	Then (92b7) from what has been established he goes on to prove what he proposed. In regard to this he does two things. First, he shows that the quod quid cannot be shown by demonstration. Secondly, that it cannot be shown by definition (9526). In regard to the first he presents three reasons, the first of which (92b7) is the following: just as a definition is brought forward to manifest something which is one in the sense that from the parts of the definition something is formed which is one per se and not one per accidens, so a demonstration which employs a definition as its middle must demonstrate something which is one; for the conclusion must be proportionate to the middle. Consequently, it is clear that one cannot in virtue of one and the same definition demonstrate things that are diverse. But the quod quid of man is one thing and his being or existence is another—for it is only in the First Principle of being, Who is being essentially, that to be and quiddity are one and the same; in all other things, which are beings by participation, the to be has to be other than the quiddity. Therefore, it is not possible to demonstrate both the quid and the quia with the same demonstration.
lib. 2 l. 6 n. 4 Secundam rationem ponit ibi: postea et per demonstrationem etc.; quae talis est. Secundum commune sapientum dictum, necessarium est quod omne, idest totum quod per demonstrationem demonstratur, sit ipsum quia est, nisi forte aliquis dicat quod hoc ipsum quia est sit substantia alicuius rei. Hoc autem est impossibile. Hoc enim ipsum quod est esse, non est substantia vel essentia alicuius rei in genere existentis. Alioquin oporteret quod hoc quod dico ens esset genus, quia genus est quod praedicatur de aliquo in eo quod quid. Ens autem non est genus, ut probatur in III Metaph. Et propter hoc etiam Deus, qui est suum esse, non est in genere.	Then (92b11) he presents the second reason and it is this: According to a common opinion of wise men, it is necessary that all i.e., the whole demonstrated by a demonstration, be the quia est, unless perchance someone would want to say that the quia est itself is the substance of a thing. However, this is impossible. For the to be is not the substance or essence of anything existing in a genus; otherwise it would be required that being be a genus, because a genus is something predicated in quod quia. But, as it is proved in Metaphysics III, being is not a genus. For this reason God Who is His own essence is not in a genus.
Si autem quia est esset substantia alicuius rei, simul cum aliquis ostenderet quia est, ostenderet quid est, et ita non totum quod demonstratio demonstrat, esset quia est. Illud autem est falsum. Ergo patet quod demonstratio solum demonstrat quia est. Demonstrat enim enunciationem aliquam, quae significat esse vel non esse.	Furthermore, if the quia est were the substance of any thing, then in the same breath that one shows the quia est he would be showing the quid est; consequently, the whole which a demonstrator manifests would not be the quia est. But this is false. Therefore, it is clear that demonstration manifests only the quia est, for it demonstrates some enunciation which signifies that something is or is not.
Et hoc etiam apparet in processu scientiarum. Geometra enim accipit quid significat hoc nomen triangulus, et demonstrat quod sit, puta cum demonstrat super lineam rectam datam triangulum aequilaterum constituere. Si igitur aliquis demonstraret solum quid est triangulus, praeter morem demonstrationum quibus utuntur scientiae, non demonstraret hoc totum quod est triangulum esse, sed demonstraret solum hoc quod dico triangulum. Sicut enim propter hoc quod esse non est substantia rei, ille qui demonstrat esse, hoc solum demonstrat; ita si aliquis demonstraret quid est, hoc solum demonstraret. Sequeretur igitur quod aliquis sciens per definitionem quid est, nesciret an est, quod est impossibile, ut ex praedictis patet.	This is apparent also in the way a science proceeds. For geometry assumes what the name triangle signifies, and demonstrates quod sit, as when it demonstrates that an equilateral triangle has been formed on a given straight line. Therefore, if one demonstrated merely what a triangle is apart from the method of demonstrating which the sciences employ, he would not be demonstrating this whole which is that a triangle exists, but only what I call triangle. For just as, owing to the fact that to be is not the substance of a thing, one who demonstrates to be demonstrates that and nothing more, so if someone demonstrates the quid est, that is all he demonstrates. It would follow, therefore, that someone who knew the quid est in virtue of a definition would not know an est—which is impossible in view of what has been established above.
lib. 2 l. 6 n. 5 Tertiam rationem ponit ibi: manifestum autem est secundum nunc etc.; quae per exempla consuetarum definitionum manifestat idem, quod in praecedenti ratione est conclusum, scilicet quod monstrans quid est non monstrat quia est. Unde dicit manifestum esse non solum secundum praedicta, sed etiam secundum modos terminorum, idest definitionum, quae nunc sunt in usu, quod illi qui definiunt, non manifestant quia est. Puta qui definit circulum, dicens quod est aliquid ex cuius medio lineae ad circumferentiam ductae sunt aequales, adhuc restat quaestio propter quid oporteat poni esse id quod definitur; puta propter quid oporteat poni quod sit circulus, qui praedicto modo definitur. Convenit enim aliquam similem rationem dicere montis aenei, puta quod est corpus aeneum in altum et usquequaque diffusum; et tamen adhuc restat quaerere an sit aliquid tale in rerum natura. Et hoc ideo quia termini, idest rationes definitivae, non declarant quod illud de quo assignantur, aut sit aut possibile sit esse; sed semper, assignata tali ratione, licet quaerere quare oporteat tale aliquid esse. Sic igitur patet quod impossibile est quod simul demonstretur quid est et quia est.	Then (92b18) he presents the third reason. Now this reason uses ordinary definitions as examples to manifest the same fact that was concluded in the previous reason, namely, that one who demonstrates the quid est is not demonstrating the quia est. Wherefore he says that it is clear not only in the light of the foregoing but also in view of the modes of terms, i.e., of definitions, which are presently in vogue that those who define do not manifest the quia est. For example, one who defines a circle as something all the lines from whose center to the circumference are equal, is still left with the question why there must be such a thing as he has defined, i.e., why it is necessary to posit that there exists such a thing as was defined; for example, why it is required to posit that there is a circle which is defined in the way mentioned. For it is acceptable to give a like description of a brass mountain by saying, for example, that it is a brass body which is lofty and extensive; but the task would still remain to establish whether there is such a thing in nature. And this because terms, i.e., defining notions, do not state that their counterpart either exists or is capable of existing; rather, whenever such a notion is formulated, it is legitimate to ask why such a thing should exist. Clearly then, it is impossible to demonstrate quid est and quia est simultaneously.
lib. 2 l. 6 n. 6 Deinde cum dicit: si ergo definiens demonstrat etc., ostendit quod non potest ostendi quod quid est definitione, ducendo ad inconveniens. Unde primo, ostendit quid ex hoc sequatur; secundo, ostendit illud quod sequitur esse inconveniens; ibi: sed inconveniens et cetera.	Then (92b26) by leading to something absurd, he shows that the quod quid cannot be shown by demonstration. First, therefore, he shows what would follow from this. Secondly, he shows that what does follow is unacceptable (92b28).
Dicit ergo primo quod, cum ille qui definit, possit ostendere vel quid est, vel tantum quid significat nomen, non propter hoc oportebit quod definitio sit manifestativa ipsius quod quid est, quod proprie ad definitionem pertinet: alioquin sequetur quod definitio significans quod quid est, nihil sit aliud quam ratio significans idem quod nomen: non enim super talem rationem addit aliquid definitio, nisi quia significat essentiam alicuius rei. Unde si non sit aliqua res, cuius essentiam definitio significet, nihil differt definitio a ratione exponente significationem alicuius nominis.	He says therefore (92b26) that since a definer might show either the quid est or merely what a name signifies, it follows that a definition does not necessarily manifest the quod quid, which belongs to definition in the proper sense; otherwise, it will follow that a definition signifying quod quid is nothing more than a statement signifying in the same way that a name does: for the only thing that a definition adds to such a notion is that it signifies the essence of some thing. Hence, if there is no thing whose essence the definition signifies, it will be no different from a statement explaining the signification of some name.
lib. 2 l. 6 n. 7 Deinde cum dicit: sed inconveniens est etc., ostendit inconveniens esse quod definitio nihil sit aliud quam ratio exponens nominis significationem. Et hoc tribus rationibus. Quarum prima est, quia contingit etiam ea quae nec sunt substantia, nec sunt universaliter entia, aliquo nomine significare. Quodlibet autem nomen per aliquam interpretationem exponi potest. Si ergo nihil aliud esset definitio quam ratio interpretativa nominis, sequeretur quod definitio posset esse non substantiarum et totaliter non entium. Quod patet esse falsum. Ostensum est enim in VII Metaph. quod definitio principaliter quidem est substantiae, aliorum autem in quantum se habent ad substantiam.	Then (92b28) he shows that it is unacceptable for a definition to be nothing more than a statement explaining the signification of a name: and this for three reasons. The first of these is that it happens that even things which are neither substances nor beings in a universal sense can be signified by a name. Now a name can be explained by some interpretation. Consequently, if a definition were nothing more than a statement interpreting a name, it would follow that a definition could be given of non-substances and of things that do not exist at all. But this is clearly false, for as 4t is shown in Metaphysics VII, definition bears principally on substance and on other things insofar as they are related to substance.
lib. 2 l. 6 n. 8 Secundam rationem ponit ibi: amplius omnes rationes etc.; quae talis est. Cuilibet rationi, idest orationi aliquid significanti, est imponere aliquod nomen ei correspondens, quod per illam rationem manifestatur. Si ergo nihil aliud sit definitio quam ratio interpretativa nominis, sequeretur quod omnes rationes essent definitiones: et ita sequetur quod, cum disputamus vel colloquimur ad invicem, ipsae disputationes vel collocutiones nostrae sint quaedam definitiones; et similiter sequetur quod Ilias, idest poema Homeri de bello Troiano, sit quaedam definitio.	Then (92b30) he gives the second reason and it is this: To any notion, i.e., to any statement signifying something, it is possible to apply a corresponding name which is explained by that notion. Therefore, if a definition is nothing more than a notion explaining a name, it would follow that all notions were definitions. As a consequence, it would follow that when we dispute or converse with anyone, the disputations or our discussions are definitions; similarly, it would follow that the Iliad, i.e., Homer’s poem about the Trojan War, is a definition.
lib. 2 l. 6 n. 9 Tertiam rationem ponit ibi: amplius neque una scientia etc.; quae talis est. Nulla scientia demonstrat quod tale nomen significet talem rem. Nomina enim significant ad placitum; unde oportet hoc supponere secundum voluntatem instituentis. Manifestum est autem quod in qualibet scientia dantur aliquae definitiones. Manifestum est ergo quod definitiones non significant hoc, scilicet solam nominis interpretationem.	Then (92b32) he gives the third reason and it is this: No science demonstrates that a given name signifies a given thing. For names are arbitrary i signs; hence they must be used according to the will of the one inventing them. But it is obvious that definitions are given in every science. Therefore, it is obvious that definitions do not signify this, i.e., a mere interpretation of a name.
lib. 2 l. 6 n. 10 Deinde cum dicit: ex his igitur neque definitio etc., epilogat quae disputative praemissa sunt. Et dicit quod ex praemissis videtur sequi quod definitio et syllogismus non sunt idem, neque de eodem; et quod definitio nihil demonstret, quia non est de eodem de quo est demonstratio. Et similiter videtur esse ostensum quod non est possibile cognoscere quod quid est, neque per definitionem, neque per demonstrationem; quia definitio solum ostendit quid, et demonstratio ostendit quia est. Sed ad cognitionem quod quid est requiritur cognitio quia est, ut dictum est.	Then (92b35) he sums up what has been so far discussed disputatively. And he says that from the foregoing it is seen to follow that definition and syllogism are neither the same nor concerned with the same; and furthermore that a definition demonstrates nothing, since it is not concerned with the same thing as a demonstration. In like manner, it seems to have been shown that it is not possible to know quod quid either by a definition or a demonstration, bcause a definition merely shows the what and a demonstration the quia. But to know the quod quid a knowledge of quia est is required, as has been shown.