Taste is both one of the senses and, by a second imposition, the name for the perfection of intellectual power (judgment). Now the clearest case of a sense power naming an intellectual power is sight. We have little need to have anyone explain what intellectual vision is. But intellectual taste is more obscure and easier to misunderstand.
Consider the English proverb “there is no arguing in matters of taste”. Given our intellectual climate, this is taken as showing that matters of taste are not objective. But this is not right- and it is not what the proverb is saying either. One cannot argue about whether pixie sticks are sweet or whether rancid meat is repugnant, but both truths are no less objective because of it. Sugar is sweet, sky is blue; four is equal to two plus two. And yet taste is still something one cannot argue about. Argument involves going from one thing to another, and while sight can show us something like this, taste cannot. We can see something going through a process, but we can’t taste it going through a process in a sense that is analogous to an argument (to taste beer at various stages of brewing, or coffee as we try to get the right amount of sugar in it, is not analogous to seeing an argument go from principles to conclusion).
So there is a certain kind of objectivity that cannot be attained by argument. Given that we can go from having this to not having it, however, we might be able to extend the word argument to name the process that gives us good taste. Now good taste arises not from arguments in the first sense of the term but from role-modeling, social constructions (like manners, etiquette, the holidays of revered figures) and (perhaps above all) the fine arts and advertising. When St. Thomas calls poetry a sort of argument, he is able to explain the way in which the objectivity of taste is developed. Note that as St. Thomas describes poetics, it has always included music and it clearly includes what we now call advertising (sc. to persuade someone about the goodness or evil of something by representing it with a certain image/ pleasing sound).
Socrates’s sharp critique of the poets and rhetoricians of his day was based on their giving bad arguments in this broad sense. Students- and no small number of their teachers- are completely bewildered by the time that Socrates devotes to attacking poets, rhetoricians, and musical modes. But Socrates tasted things more clearly than we do. Arguments that corrupt taste (low and vulgar art, advertising enticing to gluttony) are much more fatal, pernicious, and difficult to remove than any other sorts of argument.