Thomas Aquinas, Summa Theologiae

Objection 1: It would seem unlawful to kill any living thing. For the Apostle says (Rm. 13:2): "They that resist the ordinance of God purchase to themselves damnation ." Now Divine providence has ordained that all living things should be preserved, according to Ps. 146:8,9, "Who maketh grass to grow on the mountains . . . Who giveth to beasts their food." Therefore it seems unlawful to take the life of any living thing.

Objection 2: Further, murder is a sin because it deprives a man of life. Now life is common to all animals and plants. Hence for the same reason it is apparently a sin to slay dumb animals and plants.

Objection 3: Further, in the Divine law a special punishment is not appointed save for a sin. Now a special punishment had to be inflicted, according to the Divine law, on one who killed another man's ox or sheep (Ex. 22:1). Therefore the slaying of dumb animals is a sin.

On the contrary, Augustine says (De Civ. Dei i, 20): "When we hear it said, 'Thou shalt not kill,' we do not take it as referring to trees, for they have no sense, nor to irrational animals, because they have no fellowship with us. Hence it follows that the words, 'Thou shalt not kill' refer to the killing of a man."

I answer that, There is no sin in using a thing for the purpose for which it is. Now the order of things is such that the imperfect are for the perfect, even as in the process of generation nature proceeds from imperfection to perfection. Hence it is that just as in the generation of a man there is first a living thing, then an animal, and lastly a man, so too things, like the plants, which merely have life, are all alike for animals, and all animals are for man. Wherefore it is not unlawful if man use plants for the good of animals, and animals for the good of man, as the Philosopher states (Polit. i, 3).

Now the most necessary use would seem to consist in the fact that animals use plants, and men use animals, for food, and this cannot be done unless these be deprived of life: wherefore it is lawful both to take life from plants for the use of animals, and from animals for the use of men. In fact this is in keeping with the commandment of God Himself: for it is written (Gn. 1:29,30): "Behold I have given you every herb . . . and all trees . . . to be your meat, and to all beasts of the earth": and again (Gn. 9:3): "Everything that moveth and liveth shall be meat to you."

Reply to Objection 1: According to the Divine ordinance the life of animals and plants is preserved not for themselves but for man. Hence, as Augustine says (De Civ. Dei i, 20), "by a most just ordinance of the Creator, both their life and their death are subject to our use."

Reply to Objection 2: Dumb animals and plants are devoid of the life of reason whereby to set themselves in motion; they are moved, as it were by another, by a kind of natural impulse, a sign of which is that they are naturally enslaved and accommodated to the uses of others.

Reply to Objection 3: He that kills another's ox, sins, not through killing the ox, but through injuring another man in his property. Wherefore this is not a species of the sin of murder but of the sin of theft or robbery.

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod occidere quaecumque viventia sit illicitum.

Dicit enim apostolus, ad Rom. XIII, qui ordinationi dei resistit, ipse sibi damnationem acquirit.

Sed per ordinationem divinae providentiae omnia viventia conservantur, secundum illud psalm., qui producit in montibus faenum, et dat iumentis escam ipsorum.

Ergo mortificare quaecumque viventia videtur esse illicitum.

Argumentum 2

Praeterea, homicidium est peccatum ex eo quod homo privatur vita.

Sed vita communis est omnibus animalibus et plantis. Ergo eadem ratione videtur esse peccatum occidere bruta animalia et plantas.

Argumentum 3

Praeterea, in lege divina non determinatur specialis poena nisi peccato. Sed occidenti ovem vel bovem alterius statuitur poena determinata in lege divina, ut patet Exod. XXII.

Ergo occisio brutorum animalium est peccatum.

Sed Contra

Sed contra est quod Augustinus dicit, in I de CIV. Dei, cum audimus, non occides, non accipimus hoc dictum esse de fructetis, quia nullus eis est sensus, nec de irrationalibus animalibus, quia nulla nobis ratione sociantur. Restat ergo ut de homine intelligamus quod dictum est, non occides.

Corpus

Respondeo dicendum quod nullus peccat ex hoc quod utitur re aliqua ad hoc ad quod est. In rerum autem ordine imperfectiora sunt propter perfectiora, sicut etiam in generationis via natura ab imperfectis ad perfecta procedit. Et inde est quod sicut in generatione hominis prius est vivum, deinde animal, ultimo autem homo; ita etiam ea quae tantum vivunt, ut plantae, sunt communiter propter omnia animalia, et animalia sunt propter hominem. Et ideo si homo utatur plantis ad utilitatem animalium, et animalibus ad utilitatem hominum, non est illicitum, ut etiam per philosophum patet, in I polit..

Inter alios autem usus maxime necessarius esse videtur ut animalia plantis utantur in cibum, et homines animalibus, quod sine mortificatione eorum fieri non potest. Et ideo licitum est et plantas mortificare in usum animalium, et animalia in usum hominum, ex ipsa ordinatione divina, dicitur enim Gen. I, ecce, dedi vobis omnem herbam et universa ligna, ut sint vobis in escam et cunctis animantibus.

Et Gen. IX dicitur, omne quod movetur et vivit, erit vobis in cibum.

Ad 1

Ad primum ergo dicendum quod ex ordinatione divina conservatur vita animalium et plantarum non propter seipsam, sed propter hominem.

Unde ut Augustinus dicit, in I de CIV. Dei, iustissima ordinatione creatoris et vita et mors eorum nostris usibus subditur.

Ad 2

Ad secundum dicendum quod animalia bruta et plantae non habent vitam rationalem, per quam a seipsis agantur, sed semper aguntur quasi ab alio, naturali quodam impulsu. Et hoc est signum quod sunt naturaliter serva, et aliorum usibus accommodata.

Ad 3

Ad tertium dicendum quod ille qui occidit bovem alterius peccat quidem, non quia occidit bovem, sed quia damnificat hominem in re sua. Unde non continetur sub peccato homicidii, sed sub peccato furti vel rapinae.