Aristotle: The Politics: On Slavery, c. 330 BCE

Let us first speak of master and slave, looking to the needs of practical life and also seeking to attain some better theory of their relation than exists at present....Property is a part of the household, and the art of acquiring property is a part of the art of managing the household; for no man can live well, or indeed live at all, unless he be provided with necessaries. And so, in the arrangement of the family, a slave is a living possession, and property a number of such instruments; and the slave is himself an instrument which takes precedence of all other instruments.....The master is only the master of the slave; he does not belong to him, whereas the slave is not only the slave of his master, but wholly belongs to him. Hence we see what is the nature and office of a slave; he who is by nature not his own but another's man, is by nature a slave; and he may be said to be another's man who, being a human being, is also a possession. And a possession may be defined as an instrument of action, separable from the possessor.

But is there any one thus intended by nature to be a slave, and for whom such a condition is expedient and right, or rather is not all slavery a violation of nature? There is no difficulty in answering this question, on grounds both of reason and of fact. For that some should rule and others be ruled is a thing not only necessary, but expedient; from the hour of their birth, some are marked out for subjection, others for rule....Again, the male is by nature superior, and the female inferior; and the one rules, and the other is ruled; this principle, of necessity, extends to all mankind.

Where then there is such a difference as that between soul and body, or between men and animals (as in the case of those whose business is to use their body, and who can do nothing better), the lower sort are by nature slaves, and it is better for them as for all inferiors that they should be under the rule of a master. For he who can be, and therefore is, another's and he who participates in rational principle enough to apprehend, but not to have, such a principle, is a slave by nature. Whereas the lower animals cannot even apprehend a principle; they obey their instincts. And indeed the use made of slaves and of tame animals is not very different; for both with their bodies minister to the needs of life. Nature would like to distinguish between the bodies of freemen and slaves, making the one strong for servile labor, the other upright, and although useless for such services, useful for political life in the arts both of war and peace. But the opposite often happens---that some have the souls and others have the bodies of free men. And doubtless if men differed from one another in the mere forms of their bodies as much as the statues of the gods do from men, all would acknowledge that the inferior class should be slaves of the superior. It is clear, then, that some men are by nature free, and others slaves, and that for these latter slavery is both expedient and right.

There is a slave or slavery by law as well as by nature. The law of which I speak is a sort of convention---the law by which whatever is taken in war is supposed to belong to the victors. But this right many jurists impeach, as they would an orator who brought forward an unconstitutional measure: they detest the notion that, because one man has the power of doing violence and is superior in brute strength, another shall be his slave and subject. Even among philosophers there is a difference of opinion. The origin of the dispute, and what makes the views invade each other's territory, is as follows: in some sense virtue, when furnished with means, has actually the greatest power of exercising force; and as superior power is only found where there is superior excellence of some kind, power seems to imply virtue, and the dispute to be simply one about justice (for it is due to one party identifying justice with goodwill while the other identifies it with the mere rule of the stronger). If these views are thus set out separately, the other views have no force or plausibility against the view that the superior in virtue ought to rule, or be master. 

Others, clinging, as they think, simply to a principle of justice (for law and custom are a sort of justice), assume that slavery in accordance with the custom of war is justified by law, but at the same moment they deny this. For what if the cause of the war be unjust? And again, no one would ever say he is a slave who is unworthy to be a slave. Were this the case, men of the highest rank would be slaves and the children of slaves if they or their parents chance to have been taken captive and sold. Wherefore Hellenes do not like to call Hellenes slaves, but confine the term to barbarians. Yet, in using this language, they really mean the natural slave of whom we spoke at first; for it must be admitted that some are slaves everywhere, others nowhere. The same principle applies to nobility. Hellenes regard themselves as noble everywhere, and not only in their own country, but they deem the barbarians noble only when at home, thereby implying that there are two sorts of nobility and freedom, the one absolute, the other relative.

Hesiod: Works and Days, c. 750 BCE

First of all, get a house, and a woman and an ox for the plough--a slave woman and not a wife, to follow the oxen as well--and make everything ready at home, so that you may not have to ask of another, and he refuse you, and so, because you are in lack, the season pass by and your work come to nothing. 

Strabo:  Geographia, [written c. 20 A.D.], circa 550 BCE

And the temple of Aphrodite [at Corinth] was so rich that it owned more than a thousand temple slaves ---prostitutes---whom both free men and women had dedicated to the goddess. And therefore it was also on account of these temple-prostitutes that the city was crowded with people and grew rich; for instance, the ship captains freely squandered their money, and hence the proverb, "Not for every man is the voyage to Corinth."

Antiphon: On the Choreutes, c. 430 BCE

So powerful is the compulsion of the law, that even if a man slays one who is his own chattel [i.e., his slave] and who has none to avenge him, his fear of the ordinances of god and of man causes him to purify himself and withhold himself from those places prescribed by law, in the hope that by so doing he will best avoid disaster.

Demosthenes: Against Timocrates. c. 350 BCE