Aristotle, Politics

[1254a] [1] Now the tools mentioned are instruments of production, whereas an article of property is an instrument of action¹; for from a shuttle we get something else beside the mere use of the shuttle, but from a garment or a bed we get only their use. And also inasmuch as there is a difference in kind between production and action, and both need tools, it follows that those tools also must possess the same difference. But life is doing things, not making things; hence the slave is an assistant in the class of instruments of action.

And the term ‘article of property’ is used in the same way as the term ‘part’: a thing that is a part is not only a part of another thing but absolutely belongs to another thing, and so also does an article of property. Hence whereas the master is merely the slave's master and does not belong to the slave, the slave is not merely the slave of the master but wholly belongs to the master. These considerations therefore make clear the nature of the slave and his essential quality: one who is a human being belonging by nature not to himself but to another is by nature a slave, and a person is a human being belonging to another if being a man he is an article of property, and an article of property is an instrument for action separable from its owner. But we must next consider whether or not anyone exists who is by nature of this character, and whether it is advantageous and just for anyone to be a slave, or whether on the contrary all slavery is against nature. [20] And it is not difficult either to discern the answer by theory or to learn it empirically. Authority and subordination are conditions not only inevitable but also expedient; in some cases things are marked out from the moment of birth to rule or to be ruled. And there are many varieties both of rulers and of subjects （and the higher the type of the subjects, the loftier is the nature of the authority exercised over them, for example to control a human being is a higher thing than to tame a wild beast; for the higher the type of the parties to the performance of a function, the higher is the function, and when one party rules and another is ruled, there is a function performed between them）—because in every composite thing, where a plurality of parts, whether continuous or discrete, is combined to make a single common whole, there is always found a ruling and a subject factor, and this characteristic of living things is present in them as an outcome of the whole of nature, since even in things that do not partake of life there is a ruling principle, as in the case of a musical scale.² However, this matter perhaps belongs to an investigation lying somewhat outside our subject; but an animal consists primarily of soul and body, of which the former is by nature the ruling and the latter the subject factor. And to discover what is natural we must study it preferably in things that are in a natural state, and not in specimens that are degenerate. Hence in studying man we must consider a man that is in the best possible condition in regard to both body and soul, and in him the principle stated will clearly appear,—