Aristotle's Function Argument

Aristotle's function argument claims that human happiness (flourishing through living well, and not just feeling good) is rational activity in accordance with virtue. He argues that just as the good of a knife lies in cutting well, the good for humans must lie in performing our own function well, and since our function is rational activity, doing it excellently is what flourishing consists in. I think it's important to figure out whether the function tells us how to live or simply describes the nature of humans. I will argue that the argument survives the strongest objection I can raise against it, but only once we are clear about what Aristotle means by reason.

Aristotle argues that in order to understand happiness we have to first determine the function of a human. By this point in NE 1.7 he has already said that "happiness, then, is something final and self-sufficient, and is the end of action" (NE 1.7, 1097b20-21), but he admits this is a platitude and that we still need a clearer account of what happiness is (1097b22-24), and the function argument is meant to give it. Its first premise links goodness to function: "For just as for a flute-player, a sculptor, or an artist, and, in general, for all things that have a function or activity, the good and the 'well' is thought to reside in the function, so would it seem to be for man, if he has a function" (NE 1.7, 1097b25-28). In other words if the goodness of anything with a function depends on how well it performs that function, then the same must apply to humans (a good knife would be one that cuts well). But the quote ends on a condition, "if he has a function," so he still has to show that we have one. He asks whether the carpenter and the tanner can have functions while man has none, and then points out that "eye, hand, foot, and in general each of the parts evidently has a function" (1097b28-32). I think the second analogy is the stronger one since a carpenter only has his function because of his trade, whereas an eye has its function by nature as part of a living body. If organs and professionals have functions that define them, then we as a whole must also have a function, but what is that function? To him a function is the activity peculiar to a thing, so either something only it does or something it does better than anything else. Therefore to determine what it means for a human to live well we must first find what we as humans do best or uniquely, and he does this by ruling out the other candidates: "Life seems to be common even to plants, but we are seeking what is peculiar to man. Let us exclude, therefore, the life of nutrition and growth. Next there would be a life of perception, but it also seems to be common even to the horse, the ox, and every animal" (1097b33-1098a3). We can eliminate nutrition and growth as a potential function since we share this with plants. Perception can also be ruled out as a possible function as it is shared with animals (humans do grow and perceive but so does an ox). What remains is "an active life of the element that has a rational principle; of this, one part has such a principle in the sense of being obedient to one, the other in the sense of possessing one and exercising thought" (1098a3-5). He concludes the function that is unique to humans is rationality, since we reason about our wants and decisions instead of acting on instinct and we engage in theoretical thought and things like moral reasoning, which separates us from animals. So this part of the argument concludes that the human function is "an activity of soul which follows or implies a rational principle" (1098a7-8), and reason here has two parts, one that thinks and one (our desires and feelings) that can listen to thinking.

So Aristotle argues that happiness is achieved through performing our function well, but how does he get from what humans do to the highest human good? He needs a premise about the difference between a thing and a good thing of the same kind, which he gets from the lyre-player since "the function of a lyre-player is to play the lyre, and that of a good lyre-player is to do so well" (1098a11-12). A knife that cuts poorly would not be a good knife and a doctor that could not heal well would not be a good doctor, so a human who reasons poorly (unethically or irrationally) is not flourishing. The function of a good man is "the good and noble performance of these," and an action is done well "when it is performed in accordance with the appropriate excellence" (1098a14-15). Book 2 makes the role of virtue clearer when he says "the virtue of man also will be the state of character which makes a man good and which makes him do his own work well" (NE 2.6, 1106a22-24). Putting these together he concludes that "human good turns out to be activity of soul in accordance with virtue, and if there are more than one virtue, in accordance with the best and most complete" (1098a16-18), and this has to happen "in a complete life" since "one swallow does not make a summer, nor does one day" (1098a18-19). This is how he gets from a description of the function to the highest good. Happiness was already established as the chief good and the good of anything with a function is that function performed well, so happiness has to be rational activity performed well in accordance with virtue over a whole life. The clause about more than one virtue matters because Aristotle makes a distinction between two types of virtue that lines up with the two parts of the rational element: "Virtue too is distinguished into kinds in accordance with this difference; for we say that some of the virtues are intellectual and others moral" (NE 1.13, 1103a3-5). On the one hand you have intellectual virtue, which is excellence in thinking (understanding, wisdom and practical wisdom) and on the other you have moral virtue, which is excellence in acting and feeling (courage, temperance and justice). Each part of the rational element needs its own excellence, and without both a person may reason well in the abstract but fail to live virtuously. Intellectual virtue mostly comes from teaching and moral virtue from habit (NE 2.1, 1103a14-17), in the same way a good musician must practice to play excellently. Even if someone is rational that does not by itself make them happy. Every normal human is rational in the sense of having reason (which a plant or an ox doesn't) but Aristotle means reasoning well instead of irrationally, and in order to achieve happiness we must cultivate our virtuous habits over a lifetime. This raises an important question, which is what do we actually mean by rationality? If we take reason narrowly as logical deduction and abstract thinking, then it's hard to see how it alone could ground the things that make life fulfilling like emotional depth, art and friendship. If we take it broadly the way his two-part account suggests, then it may already include them. Do humans really all have the same function and does rationality by itself define a good life?

Aristotle argues that human function is rational activity, but on the narrow conception this could be too limited a way to define human life since we have many essential capacities other than reasoning such as emotional expression, creativity and our capacity to form meaningful relationships. The assumption that one function could define our whole species might oversimplify success in human life. Instead of a single function a fulfilling life could involve multiple functions working together, for example a balance of rational thought, emotional and artistic expression and practical action too. If humans have multiple functions, why should we prioritise rational activity over others? Read this way the argument prescribes too much since it ranks one capacity above the rest. The obvious way out is to say that identifying our function only describes what humans are, but just because something has a function doesn't mean that it prescribes moral duties, and this leads to the opposite problem. For example a knife's function is to cut, but does that mean that all knives must be used to cut? A knife kept purely as a decoration is still a knife but it isn't really being used as one. Even if rational activity is our function, does this mean that we must engage in rational activity? Does knowing our function really tell us how to live? I think that ethics should not simply describe human nature, but instead must prescribe what is good and how we should act and a description of human nature does not on its own tell us what is ethical and what is not. So the objection is really a dilemma, because if the function is a standard for living it prescribes too much and leaves out essential parts of being human, but if it is only a description then it prescribes nothing at all.

In response to the first horn, Aristotle would not deny that emotions, creativity and relationships are important, but would argue that rationality includes all these capacities. He would argue that rationality is not just cold logic but involves things like moral reasoning and emotions in order to reason properly, and the obedient part of the rational element is desire since "the appetitive and in general the desiring element in a sense shares in it, in so far as it listens to and obeys it" (NE 1.13, 1102b30-31). Emotions are the part of us that reason educates, which is why fear, anger and pity can be felt too much or too little and why feeling them "at the right times, with reference to the right objects, towards the right people, with the right motive, and in the right way" is characteristic of virtue (NE 2.6, 1106b18-23). Courage is feeling fear rightly rather than feeling no fear, and a musician's excellence involves their emotions in expression as well as their skill and practice. This also covers relationships, since Aristotle says "man is by nature a political animal" (Politics 1.2, 1253a2-3) because man alone has "the gift of speech" while other animals only have a voice that signals pleasure and pain (1253a9-14). Speech lets us share a sense of the just and unjust, "and the association of living beings who have this sense makes a family and a state" (1253a14-18). The Greek word Jowett translates as "speech" is the one Ross translates as "rational principle" in NE 1.7, so the family and the city are built on the very capacity the function argument picks out. Someone might say Aristotle wins by definition here, but the broad conception has a test built in, the same one the function argument used: what do plants and animals lack? Animals feel pleasure and pain but not feelings that answer to reasons, and they don't make art with deliberate form or partnerships governed by justice. If these capacities are distinctively human then they are the work of a rational principle, so this is a matter of substance and not just definitions since the objector would need a distinctively human capacity that owes nothing to reason and my examples don't qualify.

In response to the second horn, Aristotle would clarify that uniqueness and excellence do different jobs in his argument. Uniqueness only picks out which activity is the human function and excellence (a good lyre-player plays well) says what doing it well is. He doesn't say that reason is valuable just because it's unique. As for the decorative knife, Aristotle isn't deriving duties from human nature. He starts from happiness, which everyone already pursues as "the end of action" (1097b21), and asks what it consists in, so knowing our function does tell us how to live because it tells us what we are already aiming at. A person who never reasons well is still human in the same way the decorative knife is still a knife, but he misses the very thing he wants. Practical wisdom (the ability to make good and ethically correct decisions in specific situations) turns this into guidance for particular actions, since the origin "of choice is desire and reasoning with a view to an end. This is why choice cannot exist either without reason and intellect or without a moral state" (NE 6.2, 1139a31-34). This means that human action depends on both rational thought and moral character. A good life is not merely about reasoning in the abstract but about making good choices that line up with virtue. A metaphor for this would be a good general not just knowing military strategy but also how and when to apply it effectively. In this same way a good person doesn't just reason abstractly but applies the reasoning to their actual actions and choices.

Overall I think the function argument holds up better than my objection first suggested. The first horn relied on a narrow picture of reason that Aristotle doesn't hold, and the second missed that the argument starts from an end we are already pursuing. What stays open is whether his conception of reason, with one part that thinks and one part that listens, is expansive and deep enough to do justice to the whole human experience. Is there some distinctively human activity that owes nothing to reason at all? I can't think of one, but I think that is where a better objection would have to start.

Works cited

• Aristotle, Nicomachean Ethics, trans. W. D. Ross. Aristotle, Politics, trans. Benjamin Jowett. Bekker page and line numbers follow the standard Greek text.