At the end of his list of various ways of proceeding rationally, St. Thomas notes:
At other times a mere fancy inclines one to one side of a contradiction because of some representation, much as a man turns in disgust from certain food if it is described to him in terms of something disgusting. And to this is ordained the Poetics. For the poet’s task is to lead us to something virtuous by some excellent description. And all these pertain to the philosophy of the reason, for it belongs to reason to pass from one thing to another.
The quotation is well known among Thomists, but it deserves to be brought out and defended more often when the question of “rational methods”or “logical methods” arises. The “philosophy of reason” that St. Thomas describes here is clearly one that gives us movies, novels, poems, TV shows, stained glass windows, music, dance, etc. Indeed, St. Thomas is claiming that the movie, the play, the concert, etc. just is rational. As St. Thomas understands logic, the musician must be logical. This does not mean he must meditate like Spock while he strikes a chord: his very “self-expression” is something falling under the rules of logic.
It is a very old observation that human beings have both a rational part, and a part which is open to reason but in itself irrational. assume we all know what “rational part” means. What is a part open to reason but itself irrational? In the past, there is always the temptation to reduce this part to an appendage of reason, as though our goal is to make this part stop feeling and simply knock out syllogisms. This is, of course, to make this part all “openness to reason” and no “in itself irrational”, which is simply to pretend that it is not what, in fact, it is. This second part of man is not ruled by reason like an artisan rules a tool; it seems much more the case that the rational part and the irrational part must be integrated like a married couple is integrated. There are many pitfalls with this image, but one aspect that can’t be missed is that the irrational-part-open-to-reason has a contribution to make to the very function of the rational life as it exists in a human being. Anyone can see that moral life will involve some rule of the rational part, but a deeper look would show that there is also an interface and dialogue between the two parts, not such that the subrational part dominates, but nevertheless such that the subrational makes an invaluable and essential contribution to the rational.
Art- an in a special way images and music- strike immediately the irrational-part-open-to-reason. In so doing, they teach certain realities which, if they are lacking, will deeply harm our ability to reason. It is a very stunted kind of reasoner who has no awareness of the sublime or the mysterious, and both of these things are difficult to get apart from good art. The value of words is very difficult to cultivate in those who were never forced to interact with good literature. The sheer force of a word is difficult to understand to someone who does not love poetry. The length and simplicity that is required from an argument should really be modeled first from a melodic line, a sonata, a symphony, a concerto. It is very difficult to understand persons apart from idealisations of them in art, and we very often form very terrible ideas of what it is to be a human being by looking at art that shows them as they are not.