Hume's five criteria for a true judge of taste are worth slowing down on, because they are individually interesting and collectively demanding.
Delicacy of imagination is the capacity to perceive fine distinctions in aesthetic works: to notice subtleties of structure, technique, and expression that coarser perception misses. Hume uses a striking example from Don Quixote: Sancho Panza's kinsmen both taste a hogshead of wine and detect something slightly off. One says there is a taste of leather; the other says a taste of iron. Everyone laughs at them. But when the hogshead is emptied, at the bottom they find a small key with a leather thong attached. The kinsmen's delicacy was real, and the crowd's mockery was just the incomprehension of those with less refined perception.
Practice is the development of aesthetic judgment through extensive engagement with a form. Someone who has read twenty novels and someone who has read two thousand are not equally qualified to judge novels, even if their natural perceptual sensitivity is similar. Practice builds the ability to perceive relational and structural has that only emerge against the background of wide experience.
Comparison allows the critic to situate any particular work within the range of what is possible in its form, giving their judgment scale and context. The person who has only heard music from one tradition cannot reliably identify what is excellent within it, because excellence is always partly relative to the possibilities of the form.
Freedom from prejudice means approaching a work on its own terms rather than through the distorting lens of prior theoretical commitments, national loyalties, personal affiliation with the artist, or resistance to unfamiliar forms. Hume thought this was harder to achieve than it sounds, and he was right.
Taken together, these criteria produce something that sounds reasonable: we should defer, in aesthetic matters, to the judgments of people who have genuinely cultivated these capacities. Their convergent verdicts constitute the standard of taste. This is why Homer and Virgil are still considered great after two thousand years, even though no individual's taste is binding: their greatness is established by the convergent verdict of qualified readers across centuries and cultures.
But here is where things get complicated. Hume himself acknowledges two sources of legitimate aesthetic variation that seem to undermine the universality of the standard. First, differences in temperament: people have genuinely different emotional makeups, and some works will resonate more with certain temperamental types than others, without either being wrong. Second, differences in cultural context: works addressing the concerns and experiences of one age or culture will naturally speak more directly to readers of that age or culture. These are not failures of taste; they are appropriate responses to different circumstances.
The problem is that once you allow legitimate cultural and temperamental variation, it becomes very hard to say where legitimate variation ends and genuine aesthetic error begins. If a reader from a completely different cultural background genuinely cannot respond to Homer's Iliad, is that a failure of taste, or a legitimate response to cultural distance? Hume never fully resolves this, and subsequent aesthetics has been wrestling with it ever since.