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Nichomachean Ethics: Aristotle on Souls

Updated: Jul 22, 2022

Part of the Philosophy Papers series

Aristotle, in his Nicomachean Ethics, discusses the purpose of human actions and which actions specifically fulfil that purpose. Understanding the Telos of human action forms our understanding of why we ought to perform certain actions. Aristotle argues that these good actions are virtues and that virtues are broken down by the different functions of the soul. His work can also help us to understand our own nature by reflecting on the habits we form and what dispositions are being fostered within the parts of our own souls. The part of Aristotle’s work I’ll focus on is Book 1: Chapter 13, at the paragraph, starting with, ‘Of the..’ and ending at, ‘…one’s father’.

Aristotle begins by specifying the different parts of the soul. He first begins with the irrational parts of the soul, dividing them into the vegetative part and the irrational part that somewhat shares in reason. He then moves on to the rational parts of the soul, dividing them into the part that strictly has the rational principle and the part that has the tendency to obey the rational principle.

Aristotle begins by describing the vegetative division of the soul. He attributes to it the fundamental basis of life being growth and nutrition. The examples he gives are embryos and baby animals, but we can go further to add plants, microorganisms, and fungi as they also have these vegetative properties. He then clarifies that this vegetative division is not human through the following argument.

Premise 1: What we call human is that which is distinctive to humans.

Premise 2: The vegetative division of the soul is common to all life.

Conclusion: Therefore, the vegetative division of the soul is not human.

Aristotle then considers the vegetative division’s relationship to virtue. He describes how this division of the soul is akin to the state of sleep. We can understand this by observing that during sleep, the human body primarily focuses on restorative bodily functions. These functions contribute to the body’s overall health, which is something we share with other forms of life. Aristotle uses this similarity to point out that we are unable to observe any differences between the goodness or badness of an individual while they are asleep. If the good and bad are indistinguishable in sleep, then the good or bad part of them must be inactive. He then uses these premises in the following argument.

Premise 1: During sleep, an individual primarily functions according to the vegetative division of their soul.

Premise 2: The part of an individual that causes them to be ‘good’ is inactive during sleep.

Conclusion: Therefore, what causes an individual to be good is not related to the vegetative division of the soul.

However, Aristotle indicates that dreams are not a part of the vegetative aspect of sleep and concludes that the dreams of virtuous people would be better than those of ordinary people because of their excellence. He then moves on from discussing the vegetative division and begins to consider the other part of the irrational soul.

Aristotle relates the irrational part of the soul that somewhat shares in reason by juxtaposing an incontinent man with a continent one. Both are praised for their actions guided by reason, but there is a part that opposes reason and fights against it. This irrational part seemingly moves involuntarily in the soul to make the individual act against the will of reason. Aristotle gives the example of someone with dysfunctional limbs that move contrary to what the person intends to illustrate how this irrational part functions. However, unlike the limbs, we cannot perceive how it acts contrary to our reason. Here is where Aristotle compares this irrational part in the continent man and the incontinent one. In the incontinent man, this irrational part doesn’t obey reason which is why he appears to have no restraint over his irrational prompts. In the continent man, this part does obey reason. While he will still have these irrational urges, he is able to control them. Yet, in the virtuous man, these irrational urges are not present because the irrational part has become perfectly in tune with reason.

Aristotle then describes the relationship between reason and the irrational part of the soul. Reason acts as a guide for the irrational soul. Aristotle gives the analogy of reason acting as a friend or a father to the irrational part rather than a pure rational principle that the irrational part follows. Instead, the rational principle persuades the irrational part through reprimands and appeals.

Finally, Aristotle briefly describes the rational part of the soul dividing it between that which contains reason principally and the other part which obeys reason. This other part contains reason through participation by its obedience.

I find Aristotle’s arguments about the divisions of the soul to be convincing. However, I disagree with some of his points. I believe St. Thomas Aquinas better illustrates that we can refer to three kinds of souls being the vegetative, the sensitive, and the intellectual. The vegetative soul is the same as how Aristotle describes it. The sensitive soul is unique to animals as they don’t contain a rational faculty but contain the irrational parts of the soul, as described by Aristotle. Lastly, the intellectual soul is unique to humans and angels, according to Aquinas (2012)[1]. These distinctions allow for animals to be distinct from plants according to their sensitive faculties. It also allows humans and angels to be distinct from animals according to their rational faculties.

I also disagree with Aristotle’s analogy of sleeping, illustrating that what makes man good can’t be found in the vegetative soul. A knife, for example, is ordered towards the end of cutting. We can accurately define a knife as being good or bad according to its purpose. However, a knife doesn’t contain a soul and yet can still be considered good or bad regardless of having a vegetative soul. Likewise, I think that while an individual is sleeping, we can still consider them to be good or bad according to their state. A parent can be judged to be good or bad according to the purpose of parenting. Likewise, while sleeping, an individual can be judged to be good or bad according to the purpose of sleeping, i.e. restoring the body. While sleeping may not be a virtue per se, neither is the knife’s ability to cut and yet we equally call them good. Therefore, we can reject the second premise of Aristotle’s argument.

However, in charity, we can improve Aristotle’s argument to make the distinctions of goodness clearer. The vegetative soul, the sensitive soul, and the rational soul are all good when they are ordered towards their telos. The vegetative soul is good according to a state, the sensitive soul is good according to its functions, and the rational soul is good according to its habits. For the vegetative soul, the state refers to its health, with healthy indicating good nutrition and growth and unhealthy indicating the opposite. For the sensitive soul, functions refer to the natural capabilities of the animal. For example, a dairy cow that can’t produce milk would have a defective capacity that it ought to have by nature. In this sense, it can be considered bad, whereas a good dairy cow can produce milk. Finally, the rational soul is good when it is virtuous and bad when it is vicious.


Aquinas, St. Thomas. 2012. Summa Theolgiae. Translated by Laurence Shapcote. edited by John Mortensen and Enrique Alarcón. Lander, Wyoming: Aquinas Institute for the Study of Sacred Doctrine.

Aristotle., W. D Ross, and Lesley Brown. 2009. The Nicomachean Ethics. Oxford: Oxford University Press.

[1] Prima Pars, Q.50 A.5 & Q.75 A.6

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