The Truth of the Human Function

Photo: Aristotle in the School of Athens by Raphael

The Truth of the Human Function

By Samantha Costello


What is the meaning of life? As humans, we have all probably pondered this question at some point in our short existences. In fact, it is my understanding that this question has plagued humanity since the beginning of time. Well, Aristotle believed that he knew the answer to this question, and he unpacks it throughout his work, Nicomachean Ethics, specifically within Book One. According to Aristotle, the meaning of human life is happiness. Aristotle doesn’t just drop this knowledge bomb and leave it at that. He actually comes up with instructions on how to achieve happiness that are founded upon definition. He concluded: “the human good turns out to be activity of the soul in accord with virtue and, if there are more virtues than one, then in accord with the best and most complete.” This statement is loaded with meaning and hard to unpack. Essentially, Aristotle believes that happiness is the highest good that every human desires and that it can only be achieved through mastery of rational thought. However, Aristotle doesn’t think that this mastery is achievable in full by humans, and that only gods can be truly happy. I take issue with this and several other arguments that Aristotle makes, although I do appreciate the logical progression of them. In this article, I will support Aristotle’s conclusion on the human good but argue against the method by which he reaches this conclusion. I will also argue that humans can, in fact, achieve happiness. I will accomplish this via a logical approach. First, I will break down and reconstruct Aristotle’s arguments and show support for his conclusion. Then, I will follow Aristotle’s argument that all things have a function or activity, but disagree that the human function is rationality. I will accomplish this by showing how achieving rationality does not always lead to happiness and by identifying other issues with rationality as the human function. 

I will begin by outlining Aristotle’s main arguments. Tasked with identifying a logical answer to the question of the meaning of human life and how it is achievable, Aristotle works through several difficult problems, building off of each of them. Aristotle identifies that all human actions are done for some end goal. By understanding this concept, Aristotle believes that we can use it to gain a greater understanding of the human purpose. A reconstruction of his argument is as follows:

  1.     Every human action will seek an end that is good.
  2.     Some actions are done for the ends of themselves while others are done for the ends of others.
  3.     There must be a highest end that we ultimately seek through all of our actions for its own sake.
  4.     The highest end is self-sufficient.
  5.     Happiness is self-sufficient and the motivator of all human actions.
  6.     Happiness is the highest good.

So, according to Aristotle, the highest good is happiness because it is self-sufficient. In other words, happiness is the universal motivator behind all human actions and everything every human does is for happiness. Aristotle’s argument thus far is logical, and I have no real issue with it just yet.

Now, happiness has been identified as the highest good. However, there is much disagreement about what happiness is. Aristotle explains how some men think happiness is surface level things like “pleasure or wealth or honor” but he disagrees (1.4, 1095a20). Well, according to Aristotle, since the purpose of human life is apparently to achieve happiness, then a person who is successful at being human is, by definition, happy. Therefore, one now must identify what it means to be human. A reconstruction of Aristotle’s argument is as follows: 

  1.     The highest good is happiness.
  2.     Every entity has a function and the good resides within that function.
  3.     Happiness resides in the function of being man.
  4.     The sole function that is unique to man is rationality.
  5.     Happiness is achieved through the successful fulfillment of rationality.
  6.     The human good is the activity of the soul in accord with virtue and, if there are more virtues than one, then in accord with the best and most complete.

To elaborate upon this argument, Aristotle realizes that in order for something to be itself, it must have a function that is specific to it, “For just as for a flute-player, a sculptor, or an artist… for all things that have a function or activity, the good is thought to reside in the function, so would it seem to be for man, if he has a function” (1.7, 1097b25). Essentially, he is saying that the good is reached through successful achievement in the function or activity of the object. Doing this function well (being good at being human) means, then, that one must attain happiness by definition. 

But what is the human function? Aristotle claims that this function must be unique to humans alone. He explains that life cannot be the human function because it “is evidently shared with plants as well, but we are looking for what is special…” (1.7, 1097b30). It cannot be perception either, because that is extended “even to the horse, the ox, and every animal” (1.7, 1098a0).  Instead, Aristotle identifies the function that is unique to man as rational thought or reason. From here, Aristotle reaches his conclusion: “the human good (happiness) turns out to be activity of the soul (the human function which is rational thought) in accord with virtue and, if there are more virtues than one, then in accord with the best and most complete…” I take no issue with the gist of this conclusion. I think Aristotle’s arguments are valid and logical and as such, it makes sense that “the human good turns out to be an activity of the soul in accord with virtue…” (1.7, 1098a15). For the sake of this paper, I will agree that the human good is happiness. However, I take issue with how Aristotle defines happiness and the idea of rationality being the human function.

Aristotle’s understanding of happiness seems flawed to me for several reasons. In Book 10, Aristotle claims that happiness is achieved through endless contemplation (because that is what is required for reaching a high level of rational thought), and that this is an act that only the gods are capable of, “Those to whom contemplation more fully belongs are more truly happy” (Nicomachean Ethics Aristotle, 1.8, 176). Additionally, children are said not to be happy due to happiness requiring a complete, contemplating life. These ideas seem obviously erroneous. In fact, the truth seems to be the opposite of this. To me, it seems as though human life seems to abide by the law of entropy, in that it tends to decline into disorder. When we are children, happiness is simple and pure. Many children wake up each day happy and can find delight in the smallest of things.  Adults,  by contrast, devote their lives to study and aren’t purely happy as children are. Sure, they know more, but part of knowing more is to know of one’s own mortality and to know of the suffering and cruelty that exists in the world and to know of bills and sickness and stress. It seems to me that happiness, to some extent, exists in naivety. Take an individual with Williams Syndrome, for example. Also known as the Happy Syndrome, Williams Syndrome is a genetic disorder characterized by cognitive delays, learning difficulties, excessive friendliness, happiness, and empathy. According to Aristotle, someone with Williams Syndrome would never reach happiness because they don’t have the capacity for study and contemplation. I recognize that Aristotle’s definition of happiness is different from my own, but I simply disagree with him on this matter. Aristotle’s definition of happiness is not the definition of happiness that I believe motivates all of my actions. I can understand how rationality might equate to knowledge and wisdom perhaps, but not happiness. For these reasons given, I think almost all humans can achieve happiness to some extent.

Now that I have addressed my issue with Aristotle’s definition of happiness, I will disagree again with Aristotle by arguing that rationality is not the human function. Since, according to Aristotle, happiness is found through the achievement of the human function, and since I just argued that what is reached through the achievement of rational thought is not happiness, then the human function must not be rationality. I will give several reasons for this.

Aristotle splits rationality into two parts, the first being self-obedience or autonomy. The other part is “possessing one and exercising thought” (Nicomachean Ethics Aristotle, 1.7, 11) Essentially, rationality consists of two distinct parts which are required to set humans apart from animals. If being happy is a matter of being good at being human, and being human requires engaging in these two parts of rationality, then, according to Aristotle, being happy is being good at engaging in these two parts of rationality.

To begin addressing the issues involved in this rationality-happiness equation, I will dissect the first part of rationality: self-obedience/autonomy. This refers to the ability of an individual to make their own decisions in accordance with thought. This seems to be referring to the idea of free will, which is the capacity humans have to make decisions based on their internal thoughts. However, if humans are found to not actually have free will, that will collapse this part of rationality. While the thought of humans not having free will sounds absurd, it is actually a possibility. While taking a neuroscience class this semester, I learned that researchers have identified signals in the brain that activate before a conscious decision is made, suggesting we arrive at decisions before we are even consciously aware of them and that this might be an unconscious process mediated by life experiences and genetics alone. Free will could genuinely be nothing more than an illusion. Moreover, what about people who are unable to be self-obedient? Take someone with Tourette Syndrome or Parkinson’s Disease for example, where they cannot control their actions despite consciously wanting to. Or what of people with obsessive compulsive disorder who do have control over their actions but can’t actually resist intrusive thoughts? Are these people incapable of achieving happiness since they are unable to self-govern? These examples may not entirely undermine this component of rationality, but I believe they shine more than enough doubt on it.

Now, without the self-obedience part of rationality, the essence of human function comes down to an individual having and exercising thought. This then is the sole distinguisher that supposedly separates humans from animals. However, today, animals are generally understood to be capable of intelligence and thought. In fact, many animals are considered to have some degree of consciousness. Indeed, decades of research on the topic of animal cognition has demonstrated that animals of a variety of specifics can think, problem solve, and act on thoughts. Therefore, with this being the sole remaining aspect of Aristotelian rationality, it becomes clear that reason alone cannot be the human function because it is no longer unique to humans.

Ultimately, I do not deny that there is something about the ability for rational thinking that seems to be uniquely human, but I don’t think achieving rationality is the key to happiness. I think there must be some other human function that is completely unique to humans that leads to happiness. Perhaps this is something like morality or having theory of mind, the ability to understand others’ mental states. Either way, I think Aristotle’s conclusion is strong and holds, but that it is ultimately misguided.


Samantha Costello (’23) is a graduate of the University of Pennsylvania who majored in cognitive science.



Aristotle, Fine, G., & Irwin, T. (2009). Aristotle: Introductory readings. Amazon. Retrieved November 21, 2022, from 

Nicomachean Ethics Aristotle – McMaster Faculty of Social Sciences. (1999). Retrieved November 21, 2022, from