The Aristotelian concept that humans aim at the highest good comes from Aristotle’s argument in Nicomachean Ethics 1.7. Throughout the text, Aristotle seeks to identify this good through an analysis of human function. In this investigation, Aristotle claims that the human good is sufficient for the soul’s rational and excellent activity. However, Aristotle’s function argument ultimately fails as he does not justify why rational activity, rather than other distinctive human capacities, should be identified as the sole human function. The strongest objection to this argument, that Aristotle assumes without argument that what is distinctive must be the function, successfully undermines the central inference needed for the argument to work. After reconstructing Aristotle’s function argument, I develop and defend this objection by illustrating how Aristotle lacks a criterion for selecting rational activity over alternative, distinctive human capacities.
In Nicomachean Ethics 1.7, Aristotle presents an argument that to identify happiness and the human good, one must first assess the human function. Aristotle first argues that the good of something, including human beings, depends on its function (1097b26-29). To know the function of a human being, one must also separate the human being’s rational part of the soul from other components of his life, including his life of nutrition, growth, and sense perception (1098a2-3). Aristotle also clarifies that the rational part of the soul consists of two parts: one part obeys reason, and the other has reason or thinks (1098a4-5). Aristotle then goes on to claim that activity is the human soul’s function, and that activity is the part of the soul that expresses or obeys reason (1098a6-7). Perhaps one of the most important parts of this argument is the premise that the excellent man’s function is to perform this activity finely and well, and a function completed well is when its completion expresses proper virtue (1098a14-16). Therefore, Aristotle claims, the human good turns out to be the soul’s activity that expresses virtue (1098a16-17). Aristotle specifies, in particular, that if there are more goods than one, the good will express the best and most complete virtue (1098a18-19). Furthermore, Aristotle believes that the function of a good thing relates to the virtue of that thing. For instance, he argues that the function F for a harpist is the same as the excellent function F for an excellent harpist (1098a8-10). This same logic applies in the case of human beings, where an excellent human being must have an excellent function F. Aristotle uses the general case of a harpist to present an analogical argument that applies in the case of human beings.
Although Aristotle’s argument is sufficient in determining the process of (i) identifying a human being’s good and (ii) demonstrating that a human being’s good is tied to his function, Aristotle fails to establish why a human being’s function is his activity. Aristotle’s justification for linking activity to the complete function of a human being likens the separation of the rational soul into two parts to the separation of human life. Just as the rational part of the soul is in two parts – one as obeying reason and the other as itself having reason – life is also spoken of in two ways: as capacity and as activity (1098a4-9). Specifically, Aristotle argues that activity is a human being’s function because it “seems to be called life to a fuller extent” (1098a7). While Aristotle succeeds in outlining his reasoning for associating human activity with human function, he fails to assess other possibilities for what human function could be. His idea of human function relies solely on the premise that human activity is life to a fuller extent, an unsupported claim. Indeed, it could be argued that human activity is the expression of reason and aligns with the Aristotelian concept of the soul’s parts. This argument, however, overlooks other parts of human life and assumes what is distinctive is automatically the function. This raises the question of why the human function cannot be simply possessing or developing reason. Even apart from the direct cognitive process of expressing reason, other functions require reason in a secondary sense, such as being social, caring for others, or producing culture. Aristotle fails to distinguish these processes from rational activity and does not elaborate on the possibility that other distinctive human traits might be part of a human being’s function. Although reason separates human beings from other living things, this does not necessarily imply that reasoning is the human function. Reason is just one of many distinctive cognitive features that separate humans from other living things, alongside other physical features such as bipedalism or opposable thumbs. From these features, there are other candidates for what the human function could be. For instance, human beings are uniquely tied to the idea of logos. A sufficient argument for what designates a human being as a good human being might be the distinctive expression of believing in divine reason and completing virtuous actions in accordance with this belief. Another possibility for the function of a human being is the superiority of moral agency over other living things. The nature of human beings to track societal norms and obligations is distinctly different from other forms of life. At no point does Aristotle give the argument that these features are secondary rather than primary.
The objection succeeds because it exposes a gap in Aristotle’s inference from what distinguishes humans to what constitutes their function. In searching for the human function, Aristotle focuses on rational activity because it is uniquely characteristic of humans, neglecting mere possession of reason, moral agency, or sociality. Specifically, he assumes that because rational activity is what most fully expresses life, it must be the human function (1098a7-8). He does not consider alternatives in the dissemination of the human function. Aristotle tends to ignore the multiple human capacities that are distinctive relative to other animals, and offers no argument that rational activity is uniquely qualified among these to be the human function. From this, we can conclude the inference from distinctive capacity to rational activity being the sole human function is unjustified. While Aristotle claims that rational activity is the human function based on the assumption that rational activity is life to a fuller extent, this claim is unsupported. His assertions do not address the premise that distinctiveness alone cannot ground function, as these qualifications would render multiple other possibilities for the existence of more human functions. Aristotle’s conclusion is that the human good turns out to be the soul’s activity that expresses virtue (1098a16-17). This conclusion depends on the human function being rational activity. If the human function has leniency to be something else, such as moral agency or possessing logos, then the argument for the human good collapses. Even if rational activity is a distinctive feature, Aristotle does not justify why it is the most essential or primary one. The analogical argument Aristotle presents, based on the excellent function F of an excellent harpist, does not justify why the human function F is rational activity compared to another human role. Even if Aristotle were to acknowledge the existence of multiple distinctive capacities, he owes a criterion for selecting among them, which he never gives. The objection responds directly to the central premise in Aristotle’s argument, destabilizing the argument as a whole. Aristotle might respond to this objection by arguing that what is distinctive about humans is not reason itself but rather the active use of reason and the ability to perform rational action. He might claim that other capacities, such as sociality and moral agency, depend on rational activity, making rational activity more fundamental. Indeed, rational activity is a powerful basis for structuring the rest of human function. If we agree with Aristotle on the premise that sociality depends on reason. This does not show reason is the human function any more than sharp teeth being necessary for biting makes killing the function of a rabid animal. In this case, Aristotle still has not provided a criterion for why the most fundamental distinctive capacity must be the function. Even in the case of other capacities, such as moral agency or the possession of logos, which may depend on reason, Aristotle gives no argument for why they are secondary rather than coequal, and the argument becomes circular. Aristotle assumes rational activity is primary to justify that rational activity is the function. Since Aristotle lacks a justification for treating rational activity as the human function rather than one distinctive capacity among many, the objection succeeds in undermining the foundation of his function argument.
In Aristotle’s function argument, he seeks to establish happiness as excellent rational activity, grounded in the human function. He does this by arguing that the human function is rational activity and, therefore, the human good is virtuous activity. The objection challenges Aristotle’s claim, arguing that distinctiveness alone does not establish function. This objection succeeds because Aristotle does not provide a principle for choosing among distinctive capacities, and the claim that activity represents “life to a fuller extent” is unsupported.