Aristotle’s function argument

In the course of discussing the egoist worry, we saw that Aristotle’s own proposal for what happiness is is presented as the conclusion of his so-called “function argument.” This name is a bit misleading, however, since Aristotle didn’t think about function in the way we tend to these days, and he doesn’t so much give an argument as gesture in the direction of one. This is not to disregard his discussion, mind you, but rather to adjust our expectations going in. Here we will unpack the argument briefly, in the hopes of addressing some common misunderstandings as well as elucidating how the function argument fits into Aristotle’s broader project in the Nicomachean Ethics.

Introducing function

Aristotle starts talking about function when trying to work out what happiness could be (NE I.7). At this point in the discussion, happiness is what we call that thing which we choose for its own sake and never for the sake of something else, but as of yet we do not know what this thing consists in. In other words, we know that happiness is the chief good of human life, but we do not know what it is yet. Recognizing this, Aristotle starts as follows:

Presumably, however, to say that happiness is the chief good seems a platitude, and a clearer account of what it is is stilled desired. This might perhaps be given, if we could first ascertain the function of man. For just as for a flute-player, a sculptor, or any 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 I.7, 1097b24ff, emphasis added)

He proposes that if we could determine the human function, then we could work out from that what human happiness is. This follows from the fact that happiness is our chief good, and the goodness of a thing resides in its function. We’ll return to this in a bit, but first we must clarify what a function is.

One way to think about function is in terms of why a thing does what it does, its purpose or use. This is probably what we think of first when reading Aristotle these days, particularly when he goes on to name occupations as examples of things with functions, to which we might be tempted to add examples of tools or instruments.

A second way of thinking about function is in terms of how a thing does what it does, its mechanisms. Korsgaard calls this a thing’s way of functioning, and describes it as follows:

Consider, for example, a complicated machine. Such a thing might have many purposes, but in [this second sense] it has only one function — one way of functioning. For instance, a computer serves a great variety of purposes, things as different as word processing, solving mathematical problems, writing music and playing chess. But to describe its function, in [this] sense, is to describe what we might call its functional construction, the mechanisms that enable it to do all these things. Superficially, we might say that its function is the electronic storage and retrieval of information according to a program, or some such thing. But in the strict sense, only someone who actually understands how computers work can tell you what their function is. (Christine Korsgaard, Aristotle’s Function Argument)

A third way to think about function is in terms of what a thing does. In this case we are not interested in merely the mechanisms by which a thing acts (as in the second way), but the usage of those mechanisms in an activity. This is a bit more tricky to talk about than the first two ways since things can often do many different things, but function, in Aristotle’s sense, is something unique. Accordingly, for this third way we pick out a particular activity performed by something, which we call its characteristic activity or proper act, and which we can think about as follows: the characteristic activity of an X is the activity it necessarily engages in insofar as it is an X.1

The characteristic activity of a professional sculptor, let’s say, is about sculpting statues for customers. This is an activity that spans across years of the sculptor’s life, and in the course of engaging in this activity the sculptor will engage in all manner of more specific activities, like communicating and haggling with particular customers, resting and reflecting, learning and practicing techniques, buying supplies, designing statues, and sculpting this or that particular statue. The sculptor needn’t be doing any of these sub-activities at any given time, but so long as they are a professional sculptor they will be engaged in that activity that subsumes all of them, and this is the characteristic activity of a sculptor.

We add the qualification “insofar as it is an X” to specify the sense in which we’re considering the individual. Someone may be a sculptor, a violinist, and a father, and so without any qualification we could say that he has three characteristic activities. But if we qualify our consideration of him to one of these things, then there will only be one corresponding function. So, if we consider him insofar as he is a sculptor, then he will have the characteristic activity we described above.

This third way of thinking about function seems to fit best with how Aristotle speaks about it. For one, he is happy to speak of “function or activity,” which suggests that he sees a close connection between the concepts, and he eventually concludes that the human function is a kind of activity. For another, the fact that he doesn’t mention tools or instruments as examples of things with functions would be strange if he has purpose or mechanism in mind (since they have both of these kinds of function), but not so if he has characteristic activity in mind (since they don’t act of themselves).

Now, we have previously offered the following analysis of activities:

… an activity is the measured exercise of powers for the sake of some end, where the end for which the activity is done determines the appropriate measure. A thing’s powers are what determine what it can and can’t do, and whenever that thing engages in an activity it does so by exercising its powers. The end for which the activity is done determines how and when those powers are to be used, which is what we refer to as their measured exercise. Thus, we can distinguish between three things: the activity, its end, and its powers.

This applies to activities in general, so it is worth thinking about what qualifications need to be added to make it into an analysis of characteristic activities. Since the ends of characteristic activities can be as varied as the ends of activities in general, and since measures will vary accordingly, it seems the best approach is to start with the powers. The powers we’re interested in are those that are relevant to the particular function we’re considering, and will correspond to the mechanisms we mentioned when discussing the second way of thinking about function. They will be the powers used in the course of the relevant function considered at the generality at which they are used. For example, both a sculptor and a pianist use the movement of their hands when engaging in their respective functions, but the powers relevant to sculpting are things like the power to mold clay, chisel stone, hammer with the appropriate delicacy, and so on, while the powers relevant to piano-playing are things like quick finger movement, timing, applying different amounts of pressure for different volumes, and so on. When we consider powers at the generality of their being used by an X, we will call them the powers “of an X,” so that we can say that what makes an activity characteristic of an X is that it involves the measured exercise of the powers of an X.

On reflection, although function is first and foremost concerned with activity, both purpose and mechanism have something resembling them in the complete picture, in the form of the activity’s end and powers respectively.

That there is a human function

Given that function is to be understood in terms of characteristic activity, Aristotle’s inquiry is whether there is an activity characteristic of humans. In some sense it is clear that there is, since no matter what a human does, they must of necessity engage in the activity of human life. But Aristotle gestures toward a pair of arguments for this conclusion in addition to whatever intuitions we may have about it. We say, “gesture” because he really phrases it more as a pair of rhetorical questions:

Have the carpenter, then, and the tanner certain functions or activities, and has man none? Is he born without a function? Or as eye, hand, foot, and in general each of the parts evidently has a function, may one lay it down that man similarly has a function apart from all these?

Now, it’s possible that he is using occupations and organs as a way of highlighting the intuitions we just mentioned, rather than as a pair of arguments. But, if he is gesturing towards arguments, then one way to reconstruct them is in terms of unity.

While the occupations humans engage in might differ from one another in various ways, there is nevertheless unity between them insofar as they all involve the same fundamental actions, like deliberation, communication, bodily movement, sensation, learning, and so on. While these actions may be expressed in different ways and to different degrees, their pervasiveness points to a deeper activity that underlies all human occupations. And this is evident also in the fact that someone who is a carpenter could equally have been a tanner had they desired, or could switch from being a carpenter to being a tanner, or could even have both occupations simultaneously. The possibility of someone switching between (or having) multiple occupations while remaining the same human suggests that there is some activity that underlies them. And since this could in principle happen between any pair of occupations, this underlying activity must be broad enough to encompass anything a human might do, which must surely be the human function.

The argument from organs proceeds slightly differently. The activities of my eyes and heart are unified with one another in a way that the activities my eyes and your heart are not. And the same goes for any pair of organs. Today we might more naturally think of the various bodily systems rather than organs, but the point remains. And it isn’t restricted to activities within the body, but applies as well to the activities of the mind, like deliberation, self-reflection, learning, and choice. Now, the unity exhibited between the activities within a human suggest that they are parts of some overarching activity, and since this would include all the activities within a human this overarching activity must be the human function.

These arguments could be seen as approaching function from the two components of activity, namely the exercise of powers and the measure of this exercise. The argument from occupations notes that all powers exercised throughout our occupations are specialized versions of the general powers we share with one another as humans, so that the human function must involve the exercise of these powers considered in their most general form. And the argument from organs notes that the unity of the various activities within the human is to be accounted for by an overarching measure by which all of these are included in a single activity that is characteristic of all human life.

What the human function is

Having concluded that there is a human function, Aristotle proceeds to state more clearly what it is:

What then can this be? Life seems to belong 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 shared even by the horse, the ox, and every animal. There remains, then, an active life of the element that has reason; of this, one part has it in the sense of being obedient to reason, the other in the sense of possessing reason and exercising thought. And, as ‘life of the rational element’ also has two meanings, we must state that life in the sense of activity is what we mean; for this seems to be the more proper sense of the term.

When determining what the human function is, we cannot ignore this or that human power as irrelevant, since the preceding arguments indicate that the human function includes all such powers. It is clear to Aristotle that the human function is a kind of life, but it is not enough to leave it at that, since there are different kinds of life and not all kinds share the same sets of powers. As we saw in the second part of our discussion on the egoist worry, the most distinctive feature of human activity is our capacity for reason, by which we perform better the activities of life we share with other living things, as well as perform activities beyond these. Reason is unique in its ability to guide us in our lives, since by it we can understand reality and self-consciously make our way through it.

Eager to include all aspects of a human life, Aristotle distinguishes two components of the life involving reason, namely the process of reasoning and the obedience to reason. The first component involves things like deliberation, reflection, and inquiry, while the second involves acting and feeling in accordance with the results of the first. These two components working together cover the whole of the human function, albeit in a very broad way. His goal at this point is less about giving all the details and more about drawing an outline around everything.2

At the end of the passage he refers to the life of the rational element, saying that there are two senses of this. One way to think of life is as a state that is possessed, as when we say someone has a life or that they are alive. Another way to think of life is as an activity that we engage in, as when we say someone is living well or that they have made a success of their life. Aristotle refers to this distinction in order to clarify which sense of life he has in mind when discussing the human function: it does not consist simply in the possession of a state or set of properties, but in the activity of the element that has reason.

But what is this “rational element” that he speaks of, this “element that has reason”? Well, it is not a way of speaking about the process of reasoning to the exclusion of obedience to reason, since according to Aristotle these are both components of the activity of the rational element. A better way to think of it is as that aspect of all living things that makes them alive, and which in humans also includes the capacity for reason. Aristotle refers to this as the soul of a living thing, which isn’t some immaterial thing that drives the body, but the organizing process of the body which results in the activity of life in the living thing.3 The point of focusing on the soul here is to emphasize that the human function resides in the activity of the element that animates the body, rather than in the body which by itself is passive and unanimated.

Function and good

So far we have determined that there is a human function and stated in broad terms what it is, but if this is to be of any value to us in the study of ethics then we need to explain how function is connected with goodness. Accordingly, Aristotle proceeds to summarize his account of human function and introduce the connection between function and goodness:

Now if the function of man is an activity of soul which follows or implies reason, and if we say ‘a so-and-so’ and ‘a good so-and-so’ have a function which is the same in kind, eg. a lyre-player and a good lyre-player, and so without qualification in all cases, eminence in respect of goodness being added to the name of the function (for the function of a lyre-player is to play the lyre, and that of a good lyre-player is to do so well)…

His point is that if some X has a function, then it is a good X to the extent that it performs its function well. This is what Aristotle meant earlier when he said that, “for all things that have a function or activity, the good and the ‘well’ is thought to reside in the function.” On the face of it, though, this might seem a bit problematic: since “well” is the adverb of “good,” does this not really amount to a tautology, namely that an X is good if it is a good X? Now, while his point is not particularly deep — it’s stated as something obvious on the way to something further — it does not amount to a tautology. There are all sort of things an X might do well or badly that are not related to its function, and Aristotle’s point is that these are irrelevant when judging its goodness as an X. A violin-player, for instance, might be tall and therefore good at reaching up to high shelves, but this has nothing to do with whether or not they’re a good violin-player. A sculptor might be good at wall-climbing or at sprinting, but it is their function as a sculptor which is relevant to whether they’re a good sculptor or not. And so too with everything that has a function.

With this connection between function and good in hand, we can use our earlier conclusions about the human function to give an outline of the human good. And this is exactly what Aristotle does next:

… if this is the case and we state the function of man to be a certain kind of life, and this to be an activity or actions of the soul implying a rational principle, and the function of a good man to be the good and noble performance of these, and if any action is well performed when it is performed in accordance with the appropriate virtue: if this is the case, human good turns out to be activity of soul exhibiting virtue, and if there are more than one virtue, in accordance with the best and most complete.

Applying the connection between function and good, Aristotle notes that the function of the good human must be the good and noble performance of the activities of the soul involving reason.4 He then reframes this in terms of “virtue,” with what amounts to a definition of the idea: a virtue is something that enables an activity to be well-performed. Following Plato and those before him, Aristotle recognizes that happiness (the chief human good) must involve virtue in some way, and this is how he incorporates it into his own account of happiness — as a clarification of what he had previously said.

The place of the function argument

The function argument is given at the beginning of Aristotle’s investigation into happiness and goodness, as a starting point and frame for what will follow. We should not be too surprised, then, that by the end of giving the argument we have only a vague outline of what we seek. In the remainder of the first book, he will deal with some outstanding issues regarding the concept of happiness. In books II–V he will give an analysis of virtue, discuss the role of freedom in happiness, and discuss the various moral virtues, with justice getting a book for itself. Then in book VI he will discuss the intellectual virtues. These two classes of virtue have to do with following and exercising reason respectively, a division that arose during the function argument. And after dealing with the virtues, he will move to more general topics. In book VII he will discuss the different ways one’s knowledge might be odds with one’s passions, and in books VIII and IX he will discuss the nature and importance of friendship. Finally, in book X, he will bring it all together into an account of happiness that incorporates the insights gained along the way.


  1. Put more tersely, the function of an X is the per se activity qua X.
  2. As he says, “Let this serve as an outline, for we must presumably first sketch it roughly, and then later fill in the details.”
  3. It’s actually slightly more complicated than this, but the details of this do not concern us here. We discussed this with more nuance in our earlier post on the threefold whole.
  4. Attentive readers might notice that whereas earlier Aristotle referred to the human function as the activity of soul that implies or follows reason, here he refers to it as the activity of soul that implies a rational principle. Really, these amount to the same thing, since even when an activity follows reason it implies a source (principle) of that reason (rational).

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