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Thomas Says: Killing Plants and Animals

September 3rd, 2009 | 2 min read

By Gary Hartenburg

As a way of getting my blogging going, I thought I’d start a series of posts on some teachings of Thomas Aquinas.  I think this will be interesting (at least to me) because Thomas covers so much material in easy-to-digest portions and because his Summa is available online.  So today, let’s start—for no specific reason—with his argument about killing plants and animals.

Thomas says that it is not a sin to kill plants and animals to use as food.  His basic argument is that “there is no sin in using a thing for the purpose for which it is.”  Since the purpose of plants and animals, which are both imperfect in comparison with human beings, is to be useful to human beings, a human being does no wrong in killing either plant or animal if he needs to use either of them.  Thomas thinks that the purpose of plants and animals is to be useful to human beings because “the order of things is such that the imperfect are for the perfect.”

The reasoning about the order of things in this particular case is based on Aristotle’s conception of the different kinds of soul.  I suppose if someone thinks Aristotle’s wrong about the soul, they won’t find Thomas’s arguments persuasive.

Thomas also has an argument from the Bible, namely, Genesis 1:29-30 and Genesis 9:3.  The first passage only allows eating plants.  The second allows for the eating of animals.  Some have argued that since the latter allowance is made only after the Fall, those who live after the Resurrection should no longer kill animals.  But there is no suggestion in Thomas that the allowance in Genesis 9:3 has been taken away.

It is interesting, from our point of view, that Thomas does not even mention the issue of animal pain.  Today, however, that consideration is a prominent source of arguments against the morality of killing animals.

It is also interesting, from our point of view, that Thomas does think that the question of killing plants needs to be addressed.  This is probably because from our point of view the question of killing animals is addressed as a matter of not causing pain.  Since plants do not experience pain, then we need not worry about killing them.

Thomas’s interest, however, is not in not causing pain but in taking life.  Life, as a fundamental kind of good, should always be respected.  It is this concern for life that makes the issue of killing plants a live one, one that Thomas has to address in his ethics.

There is also the point that the killing of plants and animals can be moral only if they are being used appropriately.  I think this would rule out hunting for sport (unless sport can be considered necessary or sufficiently momentous in human excellence), but it would not rule out using animals for medical testing, though it would rule out using animals for testing cosmetics.