He now proceeds to ask the question whether this “natural” slave of his hypothesis actually exists, for whom such a relation is just, or whether all slavery is contrary to nature, as some allege. He answers in the affirmative. The principle of rule and subjection he declares to be a foundation law of all life.644 Men are constituted for either condition from birth, and their development follows this natural bent.645 This law may be observed in inanimate things,646 in the natural subordinate relation of the body to the soul, of domestic animals to man, of female to male, of child to parent, and of subjects to rulers.647 Thus all who are capable only of physical service hold the same relation to higher natures as the body holds to the soul, and are slaves by nature.648 This is the only relation for which the slave is naturally fitted, since he can apprehend reason without himself possessing it, being midway between animals and truly rational men.649 Usually also nature differentiates both the bodies and the souls of freemen and slaves, suiting them to their respective spheres and functions.650
This relation of slavery, Aristotle argues, is not only natural and necessary, but also beneficial for those who are so constituted.651 Just as the body is benefited by the rule of the soul, and domestic animals by the rule of man, so it is distinctly to the advantage of the “natural slave” to be ruled by a rational master. This is universally true, wherever one class of persons is as inferior to another as is the body to the soul.652
The philosopher’s frank admissions, in which he opposes the doctrine that slavery is founded on mere force, are fatal to his first argument on the natural slave. He admits that nature does not always consummate her purpose; that the souls of freemen are sometimes found in the bodies of slaves, and vice versa;653 that it is difficult to distinguish the quality of the soul, in any event;654 that the claim that slavery is neither natural nor beneficial has in it a modicum of truth, as there are sometimes merely legal slaves, or slaves by convention;655 that slavery based on mere might without virtue is unjust;656 that captives of war may be wrongly enslaved;657