1 Objection 1: It seems that life is an operation. For nothing is divided except into parts of the same genus. But life is divided by certain operations, as is clear from the Philosopher De Anima ii, 13), who distinguishes four kinds of life, namely, nourishment, sensation, local movement and understanding. Therefore life is an operation.
1 Ad secundum sic proceditur. Videtur quod vita sit quaedam operatio. Nihil enim dividitur nisi per ea quae sunt sui generis. Sed vivere dividitur per operationes quasdam, ut patet per philosophum in II libro de anima, qui distinguit vivere per quatuor, scilicet alimento uti, sentire, moveri secundum locum, et intelligere. Ergo vita est operatio quaedam.
2 Objection 2: Further, the active life is said to be different from the contemplative. But the contemplative is only distinguished from the active by certain operations. Therefore life is an operation.
2 Praeterea, vita activa dicitur alia esse a contemplativa. Sed contemplativi ab activis non diversificantur nisi secundum operationes quasdam. Ergo vita est quaedam operatio.
3 Objection 3: Further, to know God is an operation. But this is life, as is clear from the words of Jn. 18, 3, Now this is eternal life, that they may know Thee, the only true God. Therefore life is an operation.
3 Praeterea, cognoscere Deum est operatio quaedam. Haec autem est vita, ut patet per illud Ioan. XVII, haec est autem vita aeterna, ut cognoscant te solum verum Deum. Ergo vita est operatio.
4 On the contrary, The Philosopher says De Anima ii, 37), In living things, to live is to be.
4 Sed contra est quod dicit philosophus, in II de anima, vivere viventibus est esse.
5 I answer that, As is clear from what has been said Question 17, Article 3), our intellect, which takes cognizance of the essence of a thing as its proper object, gains knowledge from sense, of which the proper objects are external accidents. Hence from external appearances we come to the knowledge of the essence of things. And because we name a thing in accordance with our knowledge of it, as is clear from what has already been said Question 13, Article 1), so from external properties names are often imposed to signify essences.
Hence such names are sometimes taken strictly to denote the essence itself, the signification of which is their principal object; but sometimes, and less strictly, to denote the properties by reason of which they are imposed. And so we see that the word body is used to denote a genus of substances from the fact of their possessing three dimensions: and is sometimes taken to denote the dimensions themselves; in which sense body is said to be a species of quantity.
The same must be said of life. The name is given from a certain external appearance, namely, self-movement, yet not precisely to signify this, but rather a substance to which self-movement and the application of itself to any kind of operation, belong naturally. To live, accordingly, is nothing else than to exist in this or that nature; and life signifies this, though in the abstract, just as the word running denotes to run in the abstract. Hence living is not an accidental but an essential predicate.
Sometimes, however, life is used less properly for the operations from which its name is taken, and thus the Philosopher says Ethic. ix, 9) that to live is principally to sense or to understand.
5 Respondeo dicendum quod, sicut ex dictis patet, intellectus noster, qui proprie est cognoscitivus quidditatis rei ut proprii obiecti, accipit a sensu, cuius propria obiecta sunt accidentia exteriora. Et inde est quod ex his quae exterius apparent de re, devenimus ad cognoscendam essentiam rei. Et quia sic nominamus aliquid sicut cognoscimus illud, ut ex supradictis patet, inde est quod plerumque a proprietatibus exterioribus imponuntur nomina ad significandas essentias rerum. Unde huiusmodi nomina quandoque accipiuntur proprie pro ipsis essentiis rerum, ad quas significandas principaliter sunt imposita, aliquando autem sumuntur pro proprietatibus a quibus imponuntur, et hoc minus proprie. Sicut patet quod hoc nomen corpus impositum est ad significandum quoddam genus substantiarum, ex eo quod in eis inveniuntur tres dimensiones, et ideo aliquando ponitur hoc nomen corpus ad significandas tres dimensiones, secundum quod corpus ponitur species quantitatis. Sic ergo dicendum est et de vita. Nam vitae nomen sumitur ex quodam exterius apparenti circa rem, quod est movere seipsum, non tamen est impositum hoc nomen ad hoc significandum, sed ad significandam substantiam cui convenit secundum suam naturam movere seipsam, vel agere se quocumque modo ad operationem. Et secundum hoc, vivere nihil aliud est quam esse in tali natura, et vita significat hoc ipsum, sed in abstracto; sicut hoc nomen cursus significat ipsum currere in abstracto. Unde vivum non est praedicatum accidentale, sed substantiale. Quandoque tamen vita sumitur minus proprie pro operationibus vitae, a quibus nomen vitae assumitur; sicut dicit philosophus, IX Ethic., quod vivere principaliter est sentire vel intelligere.
6 Reply to Objection 1: The Philosopher here takes to live to mean an operation of life. Or it would be better to say that sensation and intelligence and the like, are sometimes taken for the operations, sometimes for the existence itself of the operator. For he says Ethic. ix, 9) that to live is to sense or to understand, in other words, to have a nature capable of sensation or understanding. Thus, then, he distinguishes life by the four operations mentioned. For in this lower world there are four kinds of living things. It is the nature of some to be capable of nothing more than taking nourishment, and, as a consequence, of growing and generating. Others are able, in addition, to sense, as we see in the case of shellfish and other animals without movement. Others have the further power of moving from place to place, as perfect animals, such as quadrupeds, and birds, and so on. Others, as man, have the still higher faculty of understanding.
6 Ad primum ergo dicendum quod philosophus ibi accipit vivere pro operatione vitae. Vel dicendum est melius, quod sentire et intelligere, et huiusmodi, quandoque sumuntur pro quibusdam operationibus; quandoque autem pro ipso esse sic operantium. Dicitur enim IX Ethic., quod esse est sentire vel intelligere, idest habere naturam ad sentiendum vel intelligendum. Et hoc modo distinguit philosophus vivere per illa quatuor. Nam in istis inferioribus quatuor sunt genera viventium. Quorum quaedam habent naturam solum ad utendum alimento, et ad consequentia, quae sunt augmentum et generatio; quaedam ulterius ad sentiendum, ut patet in animalibus immobilibus, sicut sunt ostrea; quaedam vero, cum his, ulterius ad movendum se secundum locum, sicut animalia perfecta, ut quadrupedia et volatilia et huiusmodi; quaedam vero ulterius ad intelligendum, sicut homines.
7 Reply to Objection 2: By vital operations are meant those whose principles are within the operator, and in virtue of which the operator produces such operations of itself. It happens that there exist in men not merely such natural principles of certain operations as are their natural powers, but something over and above these, such as habits inclining them like a second nature to particular kinds of operations, so that the operations become sources of pleasure. Thus, as by a similitude, any kind of work in which a man takes delight, so that his bent is towards it, his time spent in it, and his whole life ordered with a view to it, is said to be the life of that man. Hence some are said to lead to life of self-indulgence, others a life of virtue. In this way the contemplative life is distinguished from the active, and thus to know God is said to be life eternal. Wherefore the Reply to the Third Objection is clear.
7 Ad secundum dicendum quod opera vitae dicuntur, quorum principia sunt in operantibus, ut seipsos inducant in tales operationes. Contingit autem aliquorum operum inesse hominibus non solum principia naturalia, ut sunt potentiae naturales; sed etiam quaedam superaddita, ut sunt habitus inclinantes ad quaedam operationum genera quasi per modum naturae, et facientes illas operationes esse delectabiles. Et ex hoc dicitur, quasi per quandam similitudinem, quod illa operatio quae est homini delectabilis, et ad quam inclinatur, et in qua conversatur, et ordinat vitam suam ad ipsam, dicitur vita hominis, unde quidam dicuntur agere vitam luxuriosam, quidam vitam honestam. Et per hunc modum vita contemplativa ab activa distinguitur. Et per hunc etiam modum cognoscere Deum dicitur vita aeterna. Unde patet solutio ad tertium.