Aristotle (384-322 BC) is one of the greatest philosophers, and his moral and political philosophy remains especially influential. But he also believed that, for some people, being enslaved was just and even beneficial for them.
How could Aristotle defend a despicable, abhorrent practice like slavery? How could someone with such philosophical insight get one of the most basic moral issues completely wrong?
Aristotle’s defense of slavery illustrates how even the most brilliant people can fail to critically examine their own beliefs and society’s customs.
1. Slavery in Ancient Greece
In ancient Athens, slaves were not citizens, and they considerably outnumbered male citizens. Greeks sometimes enslaved other Greeks in wars, but most slaves in Athens were foreigners. Slavery was hereditary, and freeing one’s slaves was rare. This extensive slave underclass gave the citizen elite time for leisure and contemplation, which was important for political participation in the Athenian democracy.
2. Aristotle’s Argument Defending Slavery
Aristotle’s defense of slavery starts with the idea that in order to be just, social norms must reflect what is natural. Accordingly, society may practice slavery if there are some people who are naturally suited to be slaves.
2.1. The Idea of a Natural Slave
In general, human beings have the capacity to reason, which allows us to regulate our appetites and impulses. Sometimes we fail to do so – against our better judgment, we give in to temptation – but in a fully-developed human being, reason rules.
But what if there were some human beings whose reason couldn’t rule in this way?
Aristotle says such people could understand the reason of others but would lack entirely their own capacity for rational deliberation. Such a person would be a natural slave, Aristotle claims, meaning that they would inherently lack the capacity to rationally direct their own lives. Such people would need to be directed by those who can rationally deliberate. Since this authority should be distributed to those most able to exercise it correctly, Aristotle argues that owning such people would be just. And since someone without the capacity for rational forethought would choose badly if left to their own devices, slavery is even beneficial for them, Aristotle argues.
2.2. Are There Any Natural Slaves?
Aristotle often discusses natural slaves hypothetically: if there are any such people, this is what would be true about them. He is aware that some deny the existence of natural slaves: some “believe that it is contrary to nature to be a master (for it is by law that one person is a slave and another free, whereas by nature there is no difference between them).”
But shockingly, Aristotle says that it is “not difficult” to show that there are natural slaves, that there are people “as different from others as body is from soul or beast from human.” It is not difficult, he claims, because the psychological deficiencies of natural slaves are physically observable: nature “tends to make the bodies of slaves and free people different too, the former strong enough to be used for necessities, the latter useless for that sort of work.” Aristotle even believes that we can often tell who is a natural slave right from the beginning of life: “From the hour of their birth, some are marked out for subjection, others for rule.”
2.3. Would This Justify Greek Slavery?
What guarantees that whoever is actually enslaved happens to be a natural slave? Most Greek slaves were enslaved by conquest, and Aristotle admits that “it is possible for wars to be started unjustly.” The same is true for those born into slavery, since Aristotle states that natural slaves can sometimes give birth to naturally free persons, and vice versa.
Nevertheless, Aristotle seems to think these cases are atypical. Moreover, Aristotle argues that non-Greeks were natural slaves, and so it would be easy to determine who was a natural slave by empirical observation.
2.4. Aristotle’s Argument in Summary
We can now see how Aristotle’s argument comes together:
P1. Slavery is just and beneficial (for the slave and for the owner) if the enslaved naturally lacks the capacity to deliberate.
P2. There are some human beings who naturally lack the capacity to deliberate.
C1. Therefore, there are some human beings whose enslavement would be just and beneficial.
P3. Those who are enslaved typically lack the capacity to deliberate.
C2. Therefore, the typical slave is enslaved justly.
3. Evaluating Aristotle’s Argument
Every one of Aristotle’s premises is questionable.
The first premise is clearly mistaken: humans who lacked the capacity to deliberate would benefit from competent guardians to look out for their welfare, not a lifetime of forced labor. Aristotle exhibits astonishing blindness to the abusive and degrading nature of slavery.
The second premise, that there are human beings who lack the capacity to deliberate, might be true in some cases – perhaps those with severe brain damage or advanced dementia – but they are certainly not who Aristotle had in mind.
The third premise is similarly mistaken: Aristotle systematically misidentifies who lacks the capacity for deliberation. It was probably true that enslaved people, forbidden real education and condemned to forced labor, did not have the intellectual abilities of the free Greek citizen. But Aristotle fails to see that this is not the inherent nature of enslaved people, but the result of slavery itself.
4. The Legacy of Aristotle’s Argument
Aristotle’s argument was one of many used throughout history to defend slavery, including in the antebellum United States. American slaveholders incorporated much of Aristotle’s argument, claiming that:
- slavery was necessary for a leisured aristocracy;
- slavery benefitted the enslaved – so-called “planter paternalism;”
- slavery was justified because some people (black people, according to racist whites) were inherently less rational and intelligent.
Slavery was pervasive in both ancient Greek society and the antebellum American south. Accordingly, privileged members of those societies were unable or unwilling to see the profound injustice of slavery. Aristotle’s defense of slavery shows that even the most brilliant philosophers can succumb to the tendency to uncritically accept the practices of one’s own society. Perhaps that same tendency exists in us as well.
 Kraut 2002 (279-280). However, it should be noted that reliable numbers are hard to come by in this case.
 This is the upshot of Aristotle’s claim that slaves are tools for action, rather than production (Politics I.4, 1254a1-13). The point of having a slave is not merely to have additional material belongings, but to enable one to act in certain ways, in this case, as a contemplative citizen.
 Politics I.5, 1254b21-23, and I.13, 1260a12-13.
 Aristotle does not deny that slaves are human beings. Rather, he argues they are a kind of subcategory of human beings. This is typical of defenses of slavery throughout history: complete and utter denial of the enslaved person’s humanity is uncommon.
 Politics I.5, 1254a22-31. See also Nicomachean Ethics Book V for Aristotle’s more general remarks on justice.
 Although Aristotle seems to think this is plausible all on its own, he does offer two arguments for it. The first is analogical:
“For the soul rules the body with the rule of a master… It is evident that it is natural and beneficial for the body to be ruled by the soul, and for the affective part to be ruled by the understanding (the part that has reason), and that it would be harmful to everything if the reverse held, or if these elements were equal. The same applies in the case of human beings with respect to the other animals” (I.5, 1254b4-10).
“For the same thing is beneficial for both part and whole, body and soul; and a slave is a sort of part of his master—a sort of living but separate part of his body. Hence, there is a certain mutual benefit and mutual friendship for such masters and slaves as deserve by nature to be so related” (I.6, 1255b9-13).
Aristotle seems to think that it is a reliable generalization that when there are natural ruling parts and natural ruled parts, it is beneficial for both the whole and the parts to be in their proper relationship.
The second is a modified form of the function argument Aristotle makes in the Nicomachean Ethics (I.7). In that argument, a good life for a human being is to be found in excellently performing the function distinctive to human beings. Aristotle argues that since reason is distinctive to human beings, a good human life is one in which someone reasons well (throughout a complete life). In the Politics, Aristotle argues that:
“those people who are as different from others as body is from soul or beast from human, and people whose task (ergon), that is to say, the best thing to come from them, is to use their bodies in this condition—those people are natural slaves. And it is better for them to be subject to this rule” (I.5, 1254b16-19).
Although reasoning is distinctive to all human beings, Aristotle claims that natural slaves have reason only in some minimal sense. Accordingly, the distinctive way in which natural slaves function is not in deliberating for themselves but rather following the deliberations of others. And since a good life for a human being is to be found in excellently performing one’s distinctive function, then a good life for a natural slave is one in which it listens to others well. Of course, this argument is irrelevant if there are in fact no natural slaves.
 In fact, Aristotle’s discussion is our main evidence that the justice of slavery in Ancient Greece was debated at all.
 Politics I.3, 1253b19-21, emphasis added. All translations are from Reeve (1998) unless otherwise indicated.
 Politics I.5, 1254a18.
 Politics I.5, 1254b16-17.
 Politics I.6, 1254b26-29.
 Politics I.5, 1254a21-22. Jowett translation.
 Politics I.6, 1255a23-24.
 Politics I.6, 1255a40-1255b1.
 I say “seems” because Aristotle is unclear on this point. He is mostly concerned with theoretical issues, so he doesn’t broach how common he thought these mismatches between legal and natural slavery were in actual Greek society. The most he concedes is that the categories of legal slave and natural slave, legally free and naturally free, do “not always” match up (Politics I.6, 1255b2-9).
 Politics I.6, 1255a28-29, where even the opponents of slavery seem only to be concerned with the slavery of fellow Greeks.
 Politics I.2, 1252b4-8.
 Miller 2017, §3.
 Aristotle claims that the natural slave “shares in reason to the extent of understanding it, but does not have it himself” (Politics I.5, 1254b23-24).
 This is also true of his claims about women, who he claims have the capacity for deliberation but are unable to let it guide their actions. Politics I.13, 1260a13.
 In fact, slaves in Athens were often skilled craftsmen and sometimes occupied what we think of as professional class positions — bankers, accountants, and low-ranking bureaucrats for the Athenian state.
 Davis 2006, 188, discusses how American slaveholders were influenced by Aristotle. That said, we cannot conclude that if Aristotle had not made his argument, slaveholders would not have made it. If Aristotle’s arguments had not existed, it probably would have been necessary for slaveholders to invent them.
 E.g., James Henry Hammond, “The Mudsill Speech,” in Finkelman 1997, 86.
 E.g., Thomas R. R. Cobb, What Is Slavery and its Foundation in the Natural Law, in Finkelman 1997, 154.
 e.g., Thomas Jefferson, Notes on the State of Virginia, in Finkelman 1997, 50.
 Thanks to Shane Gronholz, Chelsea Haramia, Peter Hunt, Tom Metcalf, and Nathan Nobis for their comments on drafts of this essay.
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Ignorance and Blame: Can Ignorance Excuse? by Daniel Miller
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Theories of Moral Considerability: Who and What Matters Morally? by Jonathan Spelman
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About the Author
Dan Lowe is a lecturer in the department of philosophy at the University of Michigan. He works on social and political philosophy, feminist philosophy, and their intersection with moral epistemology. https://sites.google.com/site/danlowe161