Aristotle: the function argument

I. From The Nicomachean Ethics

Thus it seems that happiness is something final and self-sufficing, and is the end of all that man does.

But perhaps the reader things that though no one will dispute the statement that happiness is the best thing in the world, yet a still more precise definition of it is needed.

This will best be gained, I think, by asking, What is the function of man? For as the goodness and the excellence of the piper or a sculptor, or the practiser of any art, and generally of those who have any function or business to do, lies in that function, so man's good would seem to lie in his function, if he has one.

But can we suppose that, while a carpenter and a cobbler has a function and a business of his own, man has no business and no function assigned to him by nature? Nay, surely as his several members, eye and hand and foot, plainly have each his own function, so we must suppose that man also has some function over and above all these.

What then is it?

Life evidently he has in common even with the plants, but we want that which is peculiar to him. We must exclude, therefore, the life of mere nutrition and growth.

Next to this comes the life of sense; but this too he plainly shares with horses and cattle and all kinds of animals.

There remains then the life whereby he acts — the life of his rational nature, with its two sides or divisions, one rational as obeying reason, the other rational as having and exercising reason. ...

The function of man, then, is exercise of his vital faculties (or soul) on one side in obedience to reason, and on the other side with reason.

II. Critique

Aristotle's “function argument” can be logically analysed into two separate arguments.

Man's essence

1		Man's function (form, soul) is found in his essence.
2		Man's essence is what distinguishes him from other objects (or more specifically, animals)
3		Man is distinct from animals in possessing reason.
4		Therefore, Man is a rational animal
5		Therefore, Man's function is to be rational /td>

The function argument

1		The function of a piper is to pipe
2		A good piper pipes well — that is, performs his function
3		The function of man is to be rational
4		Therefore, by analogy, the good man lives the life of reason to the greatest possible extent.
5		Therefore, the happy man lives the life of reason.

His presentation of this argument in the Nicomachean Ethics reverse the logical order of these arguments — the first argument seeks to establish what man's function is and the second infers from that a moral insight. The first argument claims to derive man's function from what distinguishes him from other animals. This, if true, would be a biological fact. The second argument seeks to infer from that fact that man is a rational animal to the value that a good man leads the life of reason. Thus, taken together, the two arguments clearly commit a fact/value fallacy. The illusory compulsion of the whole suite of arguments derives from the way an ethical principle appears to follow from a biological fact. That is, from man is a rational animal (biological fact) to, therefore, man ought to live the life of reason (ethical principle).

This fact/value gap is negotiated by a play on the meaning of the word “function”. As a statement of biological fact the term “function” is used to distinguish what biological processes a man performs that animals do not. But when the term “function” is used in the context of the “function argument” to derive an ethical principle, it is used in the sense of a “purpose”. So we have fallaciously switched from one meaning to another.

Thus, the function argument can only work if we import into it another major premise, such as, “God has ordained that man's purpose is to be rational”. Without this premise, no conclusion could follow, but no doubt this premise is disputable and could not, if true, be a mere biological fact. Thus, there is also a quibble on the meaning of the word “good”. In the phrase, “A good piper pipes well”, we can demonstrate this quibble by comparing it with another statement, such as “A good assassin assassinates effectively.” Now we see that how well you do something only makes your action better if the end to which you direct your action is a good one. Aristotle confuses the effectiveness of a means to an end with the value of the end.

In the first argument about man's essence there are specific errors or reasoning. (1) Animals do not lack reason, though they have less reason than men, men are not distinct from animals by possessing a faculty that animals altogether lack; the whole basis of the argument that man can be distinguished from animals in this way fails. (2) There is no defence of the idea that man could lead a life of reason apart from leading the life of an animal. Why may it not be that in order to live well (that is morally well), a man must lead the life of both an animal and a life of reason, for after all, he is a rational animal? Aristotle argues fallaciously from “man = animal + reason” to “man = reason”.

However, in conclusion, the main point is that from a mere biological fact about what makes man different from other animals, an ethical consequence cannot be drawn. Aristotle does commit the fact/value fallacy.