Authors/Thomas Aquinas/physics/L2/lect1

Lecture 1 WHAT IS NATURE? WHAT THINGS HAVE A NATURE? WHAT THINGS ARE ‘ACCORDING TO NATURE’?

Latin	English
	LECTURE 1 (192 b 8-193 a 8) WHAT IS NATURE? WHAT THINGS HAVE A NATURE? WHAT THINGS ARE ‘ACCORDING TO NATURE’?
lib. 2 l. 1 n. 1Postquam philosophus in primo libro determinavit de principiis rerum naturalium, hic determinat de principiis scientiae naturalis. Ea autem quae primo oportet cognoscere in aliqua scientia, sunt subiectum ipsius, et medium per quod demonstrat. Unde hic secundus liber in duas partes dividitur: in prima determinat de quibus sit consideratio scientiae naturalis; in secunda ex quibus causis demonstrat, ibi: determinatis autem his et cetera. Prima dividitur in duas: in prima ostendit quid sit natura; in secunda de quibus considerat scientia naturalis, ibi: quoniam autem determinatum est et cetera. Prima dividitur in duas: in prima ostendit quid sit natura; in secunda quot modis dicitur, ibi: videtur autem natura, et cetera. Prima dividitur in duas: in prima ostendit quid sit natura; in secunda excludit intentionem quorundam tentantium demonstrare quod natura sit, ibi: quod autem est natura et cetera. Circa primum duo facit: primo notificat naturam; secundo ea quae denominantur a natura, ibi: naturam autem habent et cetera. Circa primum tria facit: primo investigat definitionem naturae; secundo concludit eam, ibi: est igitur natura etc.; tertio exponit ipsam definitionem, ibi: dico autem non secundum accidens et cetera.	141. After the Philosopher has treated the principles of natural things in Book I, he here treats the principles of natural science. Now the things which we ought to know first in any science are its subject and the method by which it demonstrates. Hence Book II is divided into two parts. First he determines what things belong to the consideration of natural science, and secondly, where he says, ‘Now that we have established...’(194 b 16; L5 #176ff), he points out the causes from which it demonstrates. The first part is divided into two parts. First he shows what nature is. Secondly, where he says, ‘We have distinguished ...’ (193 b 23; L3 #157ff), he determines what things natural science considers. The first part is divided into two parts. First he shows what nature is. Secondly the number of ways [in which the name nature is used] is pointed out, where he says, ‘Some identify...’ (193 a 9; L2 #149ff). The first part is divided into two parts. First he shows what nature is. Secondly, where he says, ‘That nature exists ...’ (193 a 2 #148), he refutes the position of those who attempt to demonstrate that nature exists. Concerning the first part he makes two points. First he states what nature is. Secondly, where he says, ‘Things “have a nature” (192 b 33 #146), he designates those things which are called ‘nature’. Concerning the first part he makes three points. First he inquires into the definition of nature. Secondly he arrives at the definition, where he says, ‘... nature is ...’(192 b 22 #145). Thirdly, he explains this definition, where he says, ‘I say ...’ (192 b 23 #145).
lib. 2 l. 1 n. 2Dicit ergo primo quod inter omnia entia, quaedam esse dicimus a natura; quaedam vero ab aliis causis, puta ab arte vel a casu. Dicimus autem esse a natura quaelibet animalia, et partes ipsorum, sicut carnem et ossa, et etiam plantas et corpora simplicia, scilicet elementa, quae non resolvuntur in aliqua corpora priora, ut sunt terra, ignis, aer et aqua: haec enim et omnia similia a natura dicuntur esse. Et differunt haec omnia ab his quae non sunt a natura, quia omnia huiusmodi videntur habere in se principium alicuius motus et status; quaedam quidem secundum locum, sicut gravia et levia, et etiam corpora caelestia; quaedam vero secundum augmentum et decrementum, ut animalia et plantae; quaedam vero secundum alterationem, ut corpora simplicia et omnia quae componuntur ex eis. Sed ea quae non sunt a natura, sicut lectus et indumentum et similia, quae accipiunt huiusmodi praedicationem secundum quod sunt ab arte, nullius mutationis principium habent in seipsis nisi per accidens, inquantum scilicet materia et substantia corporum artificiatorum sunt res naturales. Sic igitur inquantum artificialibus accidit esse ferrea vel lapidea, habent aliquod principium motus in seipsis, sed non inquantum sunt artificiata: cultellus enim habet in se principium motus deorsum, non inquantum est cultellus, sed inquantum est ferreus.	142. He says, therefore, first that we say that of all beings some are from nature, whereas others are from other causes, for example, from art or from chance. Now we say that the following things are from nature: every sort of animal, and their parts, such as flesh and blood, and also plants and simple bodies, i.e., the elements, such as earth, fire, air and water, which are not resolved into any prior bodies. For these and all things like them are said to be from nature. All of these things differ from the things which are not from nature because all things of this sort seem to have in themselves a principle of motion and rest; some according to place, such as the heavy and the light, and also the celestial bodies, some according to increase and decrease, such as the animals and plants, and some according to alteration, such as the simple bodies and everything which is composed of them. But things which are not from nature, such as a bed and clothing and like things, which are spoken of in this way because they are from art, have in themselves no principle of mutation, except per accidents, insofar as the matter and substance of artificial bodies are natural things. Thus insofar as artificial things happen to be iron or stone, they have a principle of motion in them, but not insofar as they are artifacts. For a knife has in itself a principle of downward motion, not insofar as it is a knife, but insofar as it is iron.
lib. 2 l. 1 n. 3Sed videtur hoc non esse verum, quod secundum quamlibet mutationem rerum naturalium, principium motus sit in eo quod movetur. In alteratione enim et generatione simplicium corporum, totum principium motus videtur esse ab extrinseco agente: puta cum aqua calefit, vel aer in ignem convertitur, principium mutationis est ab exteriori agente. Dicunt ergo quidam quod etiam in huiusmodi mutationibus principium activum motus est in eo quod movetur; non quidem perfectum, sed imperfectum, quod coadiuvat actionem exterioris agentis. Dicunt enim quod in materia est quaedam inchoatio formae, quam dicunt esse privationem, quae est tertium principium naturae; et ab hoc principio intrinseco generationes et alterationes corporum simplicium naturales dicuntur. Sed hoc non potest esse: quia, cum nihil agat nisi secundum quod est in actu, praedicta inchoatio formae, cum non sit actus, sed aptitudo quaedam ad actum, non potest esse principium activum. Et praeterea, etiam si esset forma completa, non ageret in suum subiectum alterando ipsum: quia forma non agit, sed compositum; quod non potest seipsum alterare, nisi sint in eo duae partes, quarum una sit alterans et alia alterata.	143. But it does not seem to be true that in every change of natural things a principle of motion is- in that which is moved. For in the alteration and the generation of simple bodies, the whole principle of motion seems to be from an external agent. For example, when water is heated, or air is converted into fire, the principle of the change is from an external agent. Therefore, some say that even in changes of this sort an active principle of motion is in that which is moved, not perfectly, but imperfectly, which principle helps the action of the external agent. For they say that in matter there is a certain inchoateness of form, which they say is privation, the third principle of nature. And the generations and alterations of simple bodies are said to be from this intrinsic principle. But this cannot be. Since a thing acts only insofar as it is in act, the aforesaid inchoate state of form, since it is not act, but a certain disposition for act, cannot be an active principle. And furthermore, even if it were a complete form, it would not act on its own subject by ‘changing it. For the form does not act, rather the composite acts. And the composite cannot alter itself unless there are two parts in it, one of which alters, the other of which is altered.
lib. 2 l. 1 n. 4Et ideo dicendum est quod in rebus naturalibus eo modo est principium motus, quo eis motus convenit. Quibus ergo convenit movere, est in eis principium activum motus; quibus autem competit moveri, est in eis principium passivum, quod est materia. Quod quidem principium, inquantum habet potentiam naturalem ad talem formam et motum, facit esse motum naturalem. Et propter hoc factiones rerum artificialium non sunt naturales: quia licet principium materiale sit in eo quod fit, non tamen habet potentiam naturalem ad talem formam. Et sic etiam motus localis corporum caelestium est naturalis, licet sit a motore separato, inquantum in ipso corpore caeli est potentia naturalis ad talem motum. In corporibus vero gravibus et levibus est principium formale sui motus (sed huiusmodi principium formale non potest dici potentia activa, ad quam pertinet motus iste, sed comprehenditur sub potentia passiva: gravitas enim in terra non est principium ut moveat, sed magis ut moveatur): quia sicut alia accidentia consequuntur formam substantialem, ita et locus, et per consequens moveri ad locum: non tamen ita quod forma naturalis sit motor, sed motor est generans, quod dat talem formam, ad quam talis motus consequitur.	144. And so it must be said that a principle of motion is in natural things in the way in which motion belongs to them. Therefore in those things to which it belongs to move, there is an active principle of motion. Whereas in those things to which it belongs to be moved, there is a passive principle, which is matter. And this principle, insofar as it has a natural potency for such a form and motion, makes the motion to be natural. And for this reason the production of artificial things is not natural. For even though the material principle is in that which comes to be, it does not have a natural potency for such a form. So also the local motion of the celestial bodies is natural, even though it is from a separated mover, inasmuch as there is in the celestial body itself a natural potency for such a motion. However in heavy and light bodies there is a formal principle of motion. (But a formal principle of this sort cannot be called the active potency to which this motion pertains. Rather it is understood as a passive potency. For heaviness in earth is not a principle for moving, but rather for being moved.) For just as the other accidents are consequent upon substantial form, so also is place, and thus also ‘to be moved to place’. However the natural form is not the mover. Rather the mover is that which generates and gives such and such a form upon which such a motion follows.
lib. 2 l. 1 n. 5Deinde cum dicit: est igitur natura etc., concludit ex praemissis definitionem naturae hoc modo. Naturalia differunt a non naturalibus inquantum habent naturam; sed non differunt a non naturalibus nisi inquantum habent principium motus in seipsis; ergo natura nihil aliud est quam principium motus et quietis in eo in quo est primo et per se et non secundum accidens. Ponitur autem in definitione naturae principium, quasi genus, et non aliquid absolutum, quia nomen naturae importat habitudinem principii. Quia enim nasci dicuntur ea quae generantur coniuncta generanti, ut patet in plantis et animalibus, ideo principium generationis vel motus natura nominatur. Unde deridendi sunt qui volentes definitionem Aristotelis corrigere, naturam per aliquid absolutum definire conati sunt, dicentes quod natura est vis insita rebus, vel aliquid huiusmodi. Dicitur autem principium et causa, ad designandum quod non omnium motuum natura est eodem modo principium in eo quod movetur, sed diversimode, ut dictum est. Dicit autem movendi et quiescendi, quia ea quae naturaliter moventur ad locum, similiter vel magis naturaliter in loco quiescunt: propter hoc enim ignis naturaliter movetur sursum, quia naturaliter ibi est, et propter quod unumquodque et illud magis. Non tamen intelligendum est quod in quolibet quod movetur naturaliter, natura sit etiam principium quiescendi; quia corpus caeleste naturaliter quidem movetur, sed non naturaliter quiescit: sed hoc pro tanto dicitur, quia non solum motus, sed etiam quietis principium est. Dicit autem in quo est, ad differentiam artificialium, in quibus non est motus nisi per accidens. Addit autem primum, quia natura, etsi sit principium motus compositorum, non tamen primo. Unde quod animal movetur deorsum, non est ex natura animalis inquantum est animal, sed ex natura dominantis elementi. Quare autem dicat per se et non secundum accidens, exponit consequenter cum dicit: dico autem non secundum accidens. Contingit enim aliquando quod aliquis medicus est sibi ipsi causa sanitatis; et sic principium suae sanationis est in eo, sed per accidens: unde principium sanationis in eo non est natura. Non enim secundum quod sanatur habet medicinam, sed secundum quod est medicus; accidit autem eundem esse medicum et sanari; sanatur enim secundum quod est infirmus. Et ideo, quia per accidens coniunguntur, aliquando per accidens dividuntur: contingit enim alium esse medicum sanantem et alium infirmum qui sanatur. Sed principium motus naturalis est in corpore naturali quod movetur, inquantum movetur: inquantum enim ignis habet levitatem, fertur sursum. Nec dividuntur ad invicem, ut aliud sit corpus quod movetur sursum et aliud leve, sed semper unum et idem. Et sicuti est de medico sanante, ita est de omnibus artificialibus. Nullum enim eorum habet in seipso suae factionis principium: sed quaedam eorum fiunt ab extrinseco, ut domus et alia quae manu inciduntur; quaedam autem fiunt a principio intrinseco, sed per accidens, ut dictum est. Et sic dictum est quid sit natura.	145. Next where he says, ‘... nature is...’ (192 b 22), he concludes from the above the definition of nature in the following manner. Natural things differ from the non-natural insofar as they have a nature. But they differ from the non-natural only insofar as they have in themselves a principle of motion. Therefore, nature is nothing other than a principle of motion and rest in that in which it is primarily and per se and not per accidens. Now ‘principle’ is placed in the definition of nature as its genus, and not as something absolute, for the name ‘nature’ involves a relation to a principle. For those things are said to be born which are generated after having been joined to a generator, as is clear in plants and animals, thus the principle of generation or motion is called nature. Hence they are to be laughed at who, wishing to correct the definition of Aristotle, tried to define nature by something absolute, saying that nature is a power seated in things or something of this sort. Moreover, nature is called a principle and cause in order to point out that in that which is moved nature is not a principle of all motions in the same way, but in different ways, as was said above [#144]. Moreover, he says that nature is a principle ‘of motion and rest’. For those things which are naturally moved to a place, also or even more naturally rest in that place. Because of this, fire is naturally moved upward, since it is natural for it to be there. And for the same reason everything can be said to be moved naturally and to rest naturally in its place. This, however, must not be understood to mean that in everything which is moved naturally nature is also a principle of coming to rest. For a heavenly body is indeed moved naturally, but it does not naturally come to rest. But on the whole it can be said that nature is not only a principle of motion but also of rest. Further he says ‘in which it is’ in order to differentiate nature from artificial things in which there is motion only per accidens. Then he adds ‘Primarily’ because even though nature is a principle of the motion of composite things, nevertheless it is not such primarily. Hence that an animal is moved downwards is not because of the nature of animal insofar as it is animal, but because of the nature of the dominant element. He explains why he says ‘per se and not per accidens’ where he says, ‘I say “not in virtue of...”’ (192 b 24). It sometimes happens that a doctor is the cause of his own health, and so the principle of his own coming to health is in him, but per accidens. Hence nature is not the principle of his coming to health. For it is not insofar as he is cured that he has the art of medicine, but insofar as he is a doctor. Hence the same being happens to be a doctor and to be cured, and he is cured insofar as he is sick. And so because these things are joined per accidens, they are also at times separated per accidens. For it is one thing to be a doctor who cures, and another thing to be a sick person who is cured. But the principle of a natural motion is in the natural body which is moved insofar as it is moved. For insofar as fire has lightness, it is carried upward. And these two things are not divided from each other so that the lightness is different than the body which is moved upward. Rather they are always one and the same. And all artificial things are like the doctor who cures. For none of them has in itself the principle of its own making. Rather some of them come to be from something outside, as a house and other things which are carved by hand, while others come to be through an intrinsic principle, but per accidens, as was said [#142]. And so it has been stated what nature is.
lib. 2 l. 1 n. 6Deinde cum dicit: naturam autem habent etc., definit ea quae a natura denominantur. Et dicit quod habentia naturam sunt illa quae habent in seipsis principium sui motus. Et talia sunt omnia subiecta naturae: quia natura est subiectum, secundum quod natura dicitur materia; et est in subiecto, secundum quod natura dicitur forma.	146. Next where he says, ‘Things “have a nature”...’ (192 b 33), he defines those things which are given the name ‘nature’. He says that those things which have in themselves a principle of their motion have a nature. And such are all subjects of nature. For nature is a subject insofar as it is called matter, and nature is in a subject insofar as it is called form.
lib. 2 l. 1 n. 7Deinde cum dicit: secundum naturam autem sunt etc., exponit quid sit secundum naturam. Et dicit quod secundum naturam esse dicuntur tam subiecta, quorum esse est a natura, quam etiam accidentia quae in eis insunt causata ab huiusmodi principio; sicut ferri sursum non est ipsa natura, neque habens naturam, sed est causatum a natura. Et sic dictum est quid sit natura, et quid sit illud quod habet naturam, et quid sit secundum naturam.	147. Next where he says, ‘The term “according to nature” (192 b 35), he explains what is ‘according to nature’. He says that ‘to be according to nature’ is said both of subjects whose existence is from nature and also of the accidents which are in them and caused by such a principle. Thus to be carried upward is not a nature itself, nor does it have nature, but it is caused by nature. And thus it has been stated what nature is, and what it is that has nature, and what is ‘according to nature’.
lib. 2 l. 1 n. 8Deinde cum dicit: quod autem est natura etc., excludit praesumptionem quorundam volentium demonstrare quod natura sit. Et dicit quod ridiculum est quod aliquis tentet demonstrare quod natura sit, cum manifestum sit secundum sensum quod multa sunt a natura, quae habent principium sui motus in se. Velle autem demonstrare manifestum per non manifestum, est hominis qui non potest iudicare quid est notum propter se, et quid non est notum propter se: quia dum vult demonstrare id quod est notum propter se, utitur eo quasi non propter se noto. Et quod hoc contingat aliquibus, manifestum est. Aliquis enim caecus natus aliquando syllogizat de coloribus: cui tamen non est per se notum id quo utitur ut principio, quia non habet intellectum rei, sed utitur solum nominibus; eo quod cognitio nostra ortum habet a sensu, et cui deficit unus sensus, deficit una scientia. Unde caeci nati, qui nunquam senserunt colorem, non possunt aliquid de coloribus intelligere; et sic utuntur non notis quasi notis. Et e converso accidit his qui volunt demonstrare naturam esse: quia utuntur notis ut non notis. Naturam autem esse, est per se notum, inquantum naturalia sunt manifesta sensui. Sed quid sit uniuscuiusque rei natura, vel quod principium motus, hoc non est manifestum. Unde patet per hoc quod irrationabiliter Avicenna conatus est improbare Aristotelis dictum, volens quod naturam esse possit demonstrari, sed non a naturali, quia nulla scientia probat sua principia. Sed ignorantia principiorum moventium non impedit quin naturam esse sit per se notum, ut dictum est.	148. Next where he says, ‘That nature exists...’ (193 a 2), he denies the presumptuous position of those who wish to demonstrate that nature exists. He says that it is ridiculous for anyone to attempt to demonstrate that nature exists. For it is manifest to the senses that many things are from nature, which have in themselves the principle of their own motion. To wish, moreover, to demonstrate the obvious by what is not obvious is the mark of a man who cannot judge what is known in itself and what is not known in itself. For when he wishes to demonstrate that which is known in itself, he uses that which is known in itself as if it were not known in itself. And it is clear that some people do this. A man who is born blind may sometimes reason about colours. But that which he uses as a principle is not known to him per se, because he has no understanding of the thing. Rather he only uses names. For our knowledge has its origin from the senses, and he who lacks one sense, lacks one science. Hence those who are born blind, and who never sense colour, cannot understand any thing about colour. And so they use the unknown as if it were known. And the converse applies to those who wish to demonstrate that nature exists. For they use the known as if it were not known. The existence of nature is known per se, insofar as natural things are manifest to the senses. But what the nature of each thing is, or what the principle of its motion is, is not manifest. Hence it is clear from this that Avicenna, who wished that it were possible to prove the existence of nature, unreasonably attempted to disprove what Aristotle has said. However Avicenna did not wish to prove this from natural things, for no science proves its own principles. But ignorance of moving principles does not mean that the existence of nature is not known per se, as was said.