[W]e understand the Greek word for non-Greek to mean something foreign, and we can call human beings foreigners either absolutely or in relation to someone. Those who lack reason, by which we define human beings, seem absolutely foreign to the human race, and so we call those who lack reason foreigners in an absolute sense. They lack reason either because they happen to live in a climate so intemperate that it causes them to be dim-witted, or because there is an evil custom in certain lands whereby human beings are rendered irrational brutish, as it were. And it clearly comes from the power of reason that reasonable laws govern human beings, and that human beings are practiced in the art of writing. And so the fact that human beings do not establish laws, or establish unreasonable laws, and the fact that some peoples have no literary practices are signs that appropriately manifest barbarism.
But we call a human being a foreigner in relation to another when the one does not communicate with the other. And nature especially constitutes human beings to communicate with one another by speech. And so we can call those who do not understand one another's speech foreigners in relation to one another. But Aristotle here is speaking about those who are foreigners absolutely.
(Commentary on Aristotle's Politics, tr. Regan)
This is an interesting interpretation of Aristotle's writings on the barbaros, and if correct it renders his position on the right of foreigners to be enslaved a great deal more plausible. I cannot, however, make up my mind as to whether Aquinas is really just foisting his own views onto his master, since he provides little textual support for the concluding sentence. Any thoughts?