One obvious cause, why many feel not the proper sentiment of beauty, is the want of that delicacy of imagination, which is requisite to convey a sensibility of those finer emotions. This delicacy every one pretends to: Every one talks of it; and would reduce every kind of taste or sentiment to its standard. But as our intention in this essay is to mingle some light of the understanding with the feelings of sentiment, it will be proper to give a more accurate definition of delicacy, than has hitherto been attempted. And not to draw our philosophy from too profound a source, we shall have recourse to a noted story in DON QUIXOTE.
It is with good reason, says SANCHO to the squire with the great nose, that I pretend to have a judgment in wine: this is a quality hereditary in our family. Two of my kinsmen were once called to give their opinion of a hogshead, which was supposed to be excellent, being old and of a good vintage. One of them tastes it; considers it; and after mature reflection pronounces the wine to be good, were it not for a small taste of leather, which he perceived in it. The other, after using the same precautions, gives also his verdict in favour of the wine; but with the reserve of a taste of iron, which he could easily distinguish. You cannot imagine how much they were both ridiculed for their judgment. But who laughed in the end? On emptying the hogshead, there was found at the bottom, an old key with a leathern thong tied to it.
David Hume, Of the Standard of Taste. Delicacy of imagination is the ability to recognize by feel subtle qualities and features in a composition; as Hume goes on to argue, despite the fact that people vary considerably on this point with respect to their natural talents, by practice everyone can make considerable headway: wide experience, frequent examination even of the same works, and self-critique so as to remove interfering biases, give one the capacity to recognize very subtle features of any work of art, and thus to have a superior taste.
And, of course, since Hume thinks of moral judgment as a species of taste, what applies to aesthetic taste will apply, mutatis mutandis, to moral taste.
Added Later: The Don Quixote reference is to Chapter XIII, for those who like to see the original.