It is easy to see, with what views some modern authors throw out these hints to prove the natural inferiority of negroes. But let every friend to humanity pray, that they may be disappointed. Britons are famous for generosity; a virtue in which it is easy for them to excel both the Romans and the Greeks.
Let it never be said, that slavery is countenanced by the bravest and most generous people on earth; by a people who are animated with that heroic passion, the love of liberty, beyond all nations ancient or modern; and the fame of whose toilsome, but unwearied perseverance, in vindicating, at the expense of life and fortune, the sacred rights of mankind, will strike terror into the hearts of sycophants and tyrants, and excite the admiration and gratitude of all good men, to the latest posterity.
[James Beattie: Selected Philosophical Writings, James A. Harris, ed. Imprint Academic (Charlottesville, VA: 2004) 137. This is part of the excellent new series, The Library of Scottish Philosophy.]
The particular modern author Beattie has in his sights is one David Hume, and in particular, Hume's notorious footnote in the essay "Of Natural Characters":
I am apt to suspect the negroes to be naturally inferior to the whites. There scarcely ever was a civilized nation of that complexion, nor even any individual eminent either in action or speculation. No ingenious manufactures amongst them, no arts, no sciences. On the other hand, the most rude and barbarous of the whites, such as the ancient GERMANS, the present TARTARS, have still something eminent about them, in their valour, form of government, or some other particular. Such a uniform and constant difference could not happen, in so many countries and ages, if nature had not made an original distinction between these breeds of men. Not to mention our colonies, there are NEGROE slaves dispersed all over EUROPE, of whom none ever discovered any symptoms of ingenuity; though low people, without education, will start up amongst us, and distinguish themselves in every profession. In JAMAICA, indeed, they talk of one negroe as a man of parts and learning; but it is likely he is admired for slender accomplishments, like a parrot, who speaks a few words plainly.
As Beattie notes in great detail, this whole line of reasoning is complete nonsense from one end to the other. Annette Baier once tried -- half-heartedly, I'm sure -- to give a partial defense of the footnote by saying that it showed Hume's emphasis on empirical data; but any reading of Beattie's response to it blows that possibility out of the water.
Hume himself is against what he calls 'slavery'; but whenever he talks about 'slavery', it often seems that he isn't thinking of slavery but of lack of liberty under tyranny, which is a different thing. Beattie, on the other hand, is quite explicitly egalitarian; he believes that all men are created in the image of God. He's also an egalitarian when it comes to the sexes, by the way, although he doesn't (as far as I can recall) discuss the matter in any of his published writings. It comes through in one or two of his letters, however. He allows for the possibility that God might have given the sexes different strengths, but insists that, whether that be the case or not, the sexes are fundamentally equal, particularly in their rational natures.