This piece is just an introduction to Aristotle's view of happiness, some thoughts, and a potential objection to it.
In this article, I will first present Aristotle’s argument that happiness is the soul’s activity that expresses reason well, and then consider an objection it seems to face. After explaining why this objection won’t work, I conclude that Aristotle’s argument is successful.
The basic structure of Aristotle’s argument is as follows:
 Happiness is the best good. (1097b)
 What is good for something is what allows it to perform its function well. (1098a)
 Human beings must have a function. (1097b)
 The function of a human is to engage in activities that utilize reason. (1098a)
 Happiness is human activity that utilizes reason well. (1098a)
Now, I'll discuss these premises and their logical progression to .
Aristotle presents premise  as a generally agreed-upon fact, citing that all other goods are subordinate to happiness, and in essence, all of our actions are driven by the pursuit of it (1098a). But it is worth noting that the happiness Aristotle refers to here is not the contemporary understanding of it as a transient emotional state, but a translation of the Greek word “eudaimonia”, which essentially means to lead a good life.
Aristotle advocates for premise  by using craftsmen as examples, arguing that their “good” is fundamentally linked to their function. We usually measure a craftsman's value by their proficiency in their craft. A virtuoso flautist or an exceptional sculptor is deemed “good”. Thus, Aristotle posits that something's “good” lies in the quality with which it performs its unique function (1098a).
Premise  is derived from Aristotle's belief that it is unlikely for humans to be without purpose. Analogous to how specific occupations like carpenters or leather workers have their particular roles or functions, Aristotle contends that humans, in their entirety, must possess a function too; it seems implausible to think that humans are idle by nature (1097b).
Aristotle arrives at premise  by proposing that the unique function of human beings lies in their capacity to reason. He posits that our soul, which he considers the defining characteristic of humanity, enables this ability. Growth, although it differentiates us from non-living entities, is also a characteristic of plants, thus it cannot be exclusive to humans. Similarly, he argues that perception and movement aren't unique human functions since animals also possess these capabilities (1097b-1098a).
 follows from , , and . Because what is good for humans is what allows them to perform their function well, and activities that utilize reason are their function, happiness is human activity that utilizes reason well (1098a).
I will now turn to evaluating the argument. Both  and  seem to make sense, and , while only proven by analogy, still seems rational.  seems to follow logically from . But to me, it seems that  doesn’t exactly follow from the rest of the premises, and as such I would like to consider a possible objection to it.
The potential flaw in Aristotle’s argument is that there seems to be a disconnect between claiming that some good comes from humans performing their function well, and that this good must be the same as the ultimate good that is happiness.
Aristotle clearly wouldn’t say that for a carpenter, the ultimate good involves being good at carpentry. He would presumably still believe that they needed to exercise their rational capacity to truly lead a good life. But his argument for this hinges on the idea that being skilled at the craft of carpentry does bring some type of good for the carpenter ( (1097b)). So it must be the case that the excellence of his function is good for the carpenter insofar as he is a carpenter, but not insofar as he is a human. Likewise, the virtue of expressing reason is good for a human insofar as they are a human. On the surface, it seems to make sense that this “human good” is the ultimate good, but upon further inspection, it isn’t exactly clear why.
The reason that claiming the "human good" is the ultimate good rather than the good of being skilled at carpentry seems to carry more weight is because it is less specific. The “human good” applies to all humans, while the good that is the skill of carpentry only applies to carpenters. But if specificity is what determines which good is the ultimate good, and less specificity means that it holds more weight as the ultimate good, why wouldn’t Aristotle denote a good that relates to the function of both humans and animals as living beings? Finding a function insofar as one is a living being seems to be far less specific. Clearly, Aristotle can’t now claim that the ultimate good belongs to the “human good” just because it is more specific, because this would lead us to question why being a skilled carpenter is not the ultimate good, seeing as it is even more specific.
Aristotle might assert that the defining reason this “human good” is the ultimate good is because it appears to apply to all humans, and no other living things (animals). But this doesn’t seem to be necessarily true. If activities that involve rationality are the human function because they are what sets us apart from other species, what about people born with genetic defects that prevent them from partaking in rational thought? Through this logic, we would have to conclude that their function does not involve rationality, and that this so-called “human good” does not apply to them.
To maintain Aristotle’s belief he would have to claim that this ultimate good should be the good that applies to most humans while excluding all other species, though this seems to be somewhat arbitrary and may bring up questions of why majority matters when defining the ultimate good.
In this article, I presented Aristotle’s argument that happiness is the soul’s activity that expresses reason well, and considered a possible objection. After explaining how Aristotle could refute this objection, I tentatively conclude that Aristotle’s argument is successful.