In this light it is unsurprising that Beattie has no patience for Aristotle's defense of natural servitude: "It would have been more worthy of Aristotle, to have inferred man's natural and universal right to liberty, from that natural and universal passion with which men desire it, and from the salutary consequences to learning, to virtue, and to every human improvement, of which it never fails to be productive" (p. 463). And it is with this in the background that Beattie attacks Hume's comments on the superiority of the white races. He refers, of course, to Hume's infamous footnote in the essay on Natural Characters, in which Hume says,
I am apt to suspect the negroes and in general all the other species of men (for there are four or five different kinds) to be naturally inferior to the whites. There never was a civilized nation of any other complexion than white, 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 betwixt these breeds of men. Not to mention our colonies, there are Negroe slaves dispersed all over Europe, of which none ever discovered any symptoms of ingenuity; tho' 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 ‘tis likely he is admired for very slender accomplishments, like a parrot, who speaks a few words plainly.
Of this, Beattie says, "These assertions are strong; but I know not whether they have anything else to recommend them" (p. 464). He then goes through a number of the problems with this line of reasoning:
(1) Even if most of the claims were true, they wouldn't prove the superiority of white races over other races, unless it were proved that the other races, when new arts and sciences were introduced among them, were unable to understand and use them. "To civilize a nation, is a work which requires long time to accomplish" (p. 464); two thousand years ago, the white races were as barbaric and savage as one could possibly find. What matters is not who by historical accident achieved this or that art or science but the human capacity to be civilized.
(2) Hume's claims are much too strong, with all the nevers, nones, and nos. Nobody could possibly know them except by a close familiarity with races past and present. But we simply don't have anything like that historical knowledge.
(3) We have excellent reason, however, to regard all of Hume's major claims here as false, or, at best misleading. When we look at what we do know the histories of the non-white races, we find that they accomplished some extremely impressive things. There were vast and powerful empires in Peru and Mexico that could not have been run without ingenuity and organization. Coming into contact with Africans and the natives of the Americans, the whites were repeatedly introduced to art and skill of which they otherwise had no inkling. The Iroquois Five Nations had a government as eminent and noble as any. And we can say even more. Nobody could possibly think that the life of a slave is one that is very congenial to learning and ingenuity, but when we look at black slaves, who are scattered, oppressed, and working under terrible conditions, what we actually find is exactly the reverse of what Hume claims: we find extraordinary ingenuity, expressed in handicraft, music, and anything that the slaves could manage under their harsh conditions to teach themselves or pick up from others. And Beattie gets a bit sarcastic when he notes that Hume is obviously being arbitrary in his reasoning when he appeals to the lack of genius found in "Negroe slaves dispersed all over Europe":
That a negroe-slave, who can neither read nor write, nor speak any European language, who is not permitted to do any thing but what his master commands, and who has not a single friend on earth, but is universally considered and treated as if he were of a species inferior to the human;--that such a creature should so distinguish himself among Europeans, as to be talked of through the world for a man of genius, is surely no reasonable expectation. To suppose him an inferior species, because he does not thus distinguish himself, is just as rational, as to suppose any private European of inferior species, because he has not raised himself to the condition of royalty. (p. 466)
Without writing and iron-working, the Europeans would be no better off than the worst-off African tribes; but Europe did not get these because Europeans are superior. We know that extremely important inventions, like the mariner's compass or gunpowder, can originate with accidents, and even if they did require genius to achieve, the only people who can lay claim to that genius are the people who actually invented them. And, likewise, mere difference from European manners cannot be taken as evidence of ignobility. If the Iroquois were to visit Europe, they would have some very ignoble and barbaric things to write back home about.
Beattie ends his discussion of this point with an appeal to his countrymen:
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. (pp. 467-468)
It's important to understand that none of this is a mere side-issue for Beattie; he is discussing how the skepticism of his day is toxic to morals. Attacking the basic principles of human nature, skeptics like Hume take away the possibility of building our assessment of the rights and worth of human beings on their shared human nature, which is what should be the real foundation of any such discussion, forcing people instead to try to construct it out of a conglomeration of accidents, just as Hume does in his assessment of non-white races. In reality, the worth of the non-white races is found in precisely the same thing as the worth of whites: they too yearn for freedom, for happiness, for justice; they too are capable of honor and decency; they too want to know the world around them and are capable of doing so through external sense and internal sense and all the other principles of human nature. All such worth lies in one thing: that they are human, and have good sense as their common birthright. But the skeptic cannot recognize any such thing. Here we see the danger of Hume-style skepticism to morals and the moral sciences. Of course, one could fix this element in Hume, but it would be open to Beattie to point out that any such thing is an ad hoc adjustment, not flowing from the basic approach.
There is an interesting postscript here. If you look at modern versions of the essay on Natural Characters, what you will see is this version of the footnote:
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.
You will notice the revisions to the first two sentences -- these occurred in Hume's very last revision, for an edition that was published posthumously. Some people have suggested that this is in response to Beattie, and indeed hit is notable that he weakens some of his expressions and draws a more limited conclusion. However, there's no reason to think that Hume ever read Beattie closely, and clearly this footnote does not constitute anything like an adequate response to Beattie's arguments, which would require only slight modification to be just as forceful against this as against the original. So we don't actually know why Hume made the change. It's clear enough, though, that it wasn't enough of a change. And it's important to understand that there's no real excuse for it: Beattie's position wasn't unheard of, especially in Enlightenment Scotland, which did as much as, and perhaps more than, any other culture at the time to further the idea of natural rights. And Hume's reasoning here isn't very good; Beattie's third argument in particular utterly demolishes it. At the same time, however, Beattie raises an important issue. Perhaps Hume's approach does not require the conclusion he draws here (which is supposed to be based on empirical data), but there certainly seems to have been nothing to rule it out, impede it, or put it into question. And Beattie's whole point is that the skeptics of his day are dangerous in the perfectly straightforward sense that, despite their cant about opposing bigotry, when they are done, bigotry, prejudice, and arbitrary assumption is all that is left.
In any case, that's Beattie's Essay on Truth.