[55] Cf. Hor. Serm. i. 3. 82; ii. 3. 40.
[56] Cf. infra, de Cons. i. pr. 4 (p. 142) _oportet uulnus detegas.
[57] Vide supra, p. 75, and De Trin. p. 3.
I.
Natura igitur aut de solis corporibus dici potest aut de solis substantiis, id est corporeis atque incorporeis, aut de omnibus rebus quae quocumque modo esse dicuntur. Cum igitur tribus modis natura dici possit, tribus modis sine dubio definienda est. Nam si de omnibus rebus naturam dici placet, talis definitio dabitur quae res omnes quae sunt possit includere. Erit ergo huiusmodi: "natura est earum rerum quae, cum sint, quoquo modo intellectu capi possunt." In hac igitur definitione et accidentia et substantiae definiuntur; haec enim omnia intellectu capi possunt. Additum uero est "quoquo modo," quoniam deus et materia integro perfectoque intellectu intellegi non possunt, sed aliquo tamen modo ceterarum rerum priuatione capiuntur. Idcirco uero adiunximus "quae cum sint," quoniam etiam ipsum nihil significat aliquid sed non naturam. Neque enim quod sit aliquid sed potius non esse significat; omnis uero natura est. Et si de omnibus quidem rebus naturam dici placet, haec sit naturae definitio quam superius proposuimus. Sin uero de solis substantiis natura dicitur, quoniam substantiae omnes aut corporeae sunt aut incorporeae, dabimus definitionem naturae substantias significanti huiusmodi: "natura est uel quod facere uel quod pati possit." "Pati" quidem ac "facere," ut omnia corporea atque corporeorum anima; haec enim in corpore et a corpore et facit et patitur. "Facere" uero tantum ut deus ceteraque diuina. Habes igitur definitionem eius quoque significationis naturae quae tantum substantiis applicatur. Qua in re substantiae quoque est reddita definitio. Nam si nomen naturae substantiam monstrat, cum naturam descripsimus substantiae quoque est assignata descriptio. Quod si naturae nomen relictis incorporeis substantiis ad corporales usque contrahitur, ut corporeae tantum substantiae naturam habere uideantur, sicut Aristoteles ceterique et eiusmodi et multimodae philosophiae sectatores putant, definiemus eam, ut hi etiam qui naturam non nisi in corporibus esse posuerunt. Est autem eius definitio hoc modo: "natura est motus principium per se non per accidens." Quod "motus principium" dixi hoc est, quoniam corpus omne habet proprium motum, ut ignis sursum, terra deorsum. Item quod "per se principium motus" naturam esse proposui et non "per accidens," tale est, quoniam lectum quoque ligneum deorsum ferri necesse est, sed non deorsum per accidens fertur. Idcirco enim quia lignum est, quod est terra, pondere et grauitate deducitur. Non enim quia lectus est, deorsum cadit, sed quia terra est, id est quia terrae contigit, ut lectus esset; unde fit ut lignum naturaliter esse dicamus, lectum uero artificialiter. Est etiam alia significatio naturae per quam dicimus diuersam esse naturam auri atque argenti in hoc proprietatem rerum monstrare cupientes, quae significatio naturae definietur hoc modo: "natura est unam quamque rem informans specifica differentia." Cum igitur tot modis uel dicatur uel definiatur natura, tam catholici quam Nestorius secundum ultimam definitionem duas in Christo naturas esse constituunt; neque enim easdem in deum atque hominem differentias conuenire.
I.
Nature, then, may be affirmed either of bodies alone or of substances alone, that is, of corporeals or incorporeals, or of everything that is in any way capable of affirmation. Since, then, nature can be affirmed in three ways, it must obviously be defined in three ways. For if you choose to affirm nature of the totality of things, the definition will be of such a kind as to include all things that are. It will accordingly be something of this kind: "Nature belongs to those things which, since they exist, can in some measure be apprehended by the mind." This definition, then, includes both accidents and substances, for they all can be apprehended by the mind. But I add "in some measure" because God and matter cannot be apprehended by mind, be it never so whole and perfect, but still they are apprehended in a measure through the removal of accidents. The reason for adding the words, "since they exist," is that the mere word "nothing" denotes something, though it does not denote nature. For it denotes, indeed, not that anything is, but rather non-existence; but every nature exists. And if we choose to affirm "nature" of the totality of things, the definition will be as we have given it above.
But if "nature" is affirmed of substances alone, we shall, since all substances are either corporeal or incorporeal, give to nature denoting substances a definition of the following kind: "Nature is either that which can act or that which can be acted upon." Now the power to act and to suffer belongs to all corporeals and the soul of corporeals; for it both acts in the body and suffers by the body. But only to act belongs to God and other divine substances.
Here, then, you have a further definition of what nature is as applied to substances alone. This definition comprises also the definition of substance. For if the word nature signifies substance, when once we have defined nature we have also settled the definition of substance. But if we neglect incorporeal substances and confine the name nature to corporeal substances so that they alone appear to possess the nature of substance—which is the view of Aristotle and the adherents both of his and various other schools—we shall define nature as those do who have only allowed the word to be applied to bodies. Now, in accordance with this view, the definition is as follows: "Nature is the principle of movement properly inherent in and not accidentally attached to bodies." I say "principle of movement" because every body has its proper movement, fire moving upwards, the earth moving downwards. And what I mean by "movement properly inherent and not accidentally attached" is seen by the example of a wooden bed which is necessarily borne downward and is not carried downward by accident. For it is drawn downward by weight and heaviness because it is of wood, i.e. an earthly material. For it falls down not because it is a bed, but because it is earth, that is, because it is an accident of earth that it is a bed; hence we call it wood in virtue of its nature, but bed in virtue of the art that shaped it.
Nature has, further, another meaning according to which we speak of the different nature of gold and silver, wishing thereby to point the special property of things; this meaning of nature will be defined as follows: "Nature is the specific difference that gives form to anything." Thus, although nature is described or defined in all these different ways, both Catholics and Nestorians firmly hold that there are in Christ two natures of the kind laid down in our last definition, for the same specific differences cannot apply to God and man.