Kant's Critique of Judgment is organized along the lines of the ladder of love in Diotima's speech in the Symposium. Just as with Plato, there are various stages in our quest for beauty. For Kant, we start with the concepts of disinterestedness and pure beauty, move on to the idea of dependent beauty, then to the ideal of beauty, then to the intellectual interest in beauty, and end with the concept of aesthetic ideas. Section #49 which deals with aesthetic ideas is the climax of this work. It is there that Kant finally makes good on his promise in the Introduction to provide a bridge between the empirical and the supersensible realm. Most readers of Kant hardly get beyond the moment in which he introduces the idea of disinterestedness. (And this is even true recently with philosophers I otherwise deeply admire). This is like never getting beyond appreciation of the physically beautiful boy in the gymnasium in Plato's ladder of love. This is not only a distortion of our understanding of Kant but of the entire history and importance of aesthetics as a subdiscipline of philosophy.
We immediately learn that a poem can be "pretty and elegant" and yet soulless in the sense of missing what animates the mind. Disinterested perception might appreciate this poem, but it is of little real value: which indicates that mere beauty is not as important as it first seems. Soul is needed too. This animation always involves a free play of the mental powers, i.e. imagination and understanding. It strengthens those powers, allowing them to be strengthened also in their practical and cognitive usage outside of aesthetics. The play, Kant says, is both self-maintaining and also one that allows those faculties to be even more powerful in their free play.
Kant calls this principle "the faculty of presenting aesthetic ideas," i.e. representations of the mind which induce much, although no definite, thought. Language can never render the aesthetic idea "completely intelligible." Kant also tells us that the aesthetic idea is a "counterpart (pendant) of a rational idea" Rational ideas may just include or may be equivalent to ideas of transcendent things, such as the ideas of God, immortality and the soul. No intuition can ever be adequate to such ideas, which is to say that the imagination cannot fully grasp them. What it is to be a counterpart or pendant to such an idea is not immediately made clear.
We learn a lot about aesthetic ideas, however, in the next paragraph: the imagination, insofar as it is productive, "is a powerful agent for creating, as it were, a second nature out of the material supplied to it by actual nature." The artist, for example Van Gogh in his Starry Night, creates a second nature. He creates a nature in which the sky consists of streaks of blue, etc. We had learned previously that a fine artist is a genius who follows his own rules. We also learn here that the productive imagination "affords us entertainment where experience proves too commonplace." So it is not always or necessarily entirely serious. We "even use it to remodel experience" following both "laws of analogy" and principles of reason as natural to us as those followed in constructing empirical nature. And, "by this means we get a sense of our freedom from the law of association" which is dominant during that construction. It seems that the creative imagination of the artist allows us to be free: something only possible for us outside the empirical realm. So the aesthetic ideas provide a bridge from the empirical to the transcendent realm. The artist borrows from the empirical realm, from nature, to create something that "surpasses nature." (This is probably not in the sense that the product is more important than nature, only that it is different from nature.)
These representations are called "ideas" (Kant uses "idea" in a way more like Plato than like we do when we speaking of "having an idea") because they try to get beyond "the confines of experience" and to get as close as possible to presenting "rational concepts" which is to say concepts like that of God, immortality and the soul. In doing this, they give "to those concepts the semblance of an objective reality." (This is noteworthy since Kant, as always, is not committed the referents of these concepts actually existing. Kant, although probably not an agnostic or a Deist often says things consistent not only with those views but also with atheism, as I have often argue in this blog.) But, as Kant observes "no concept can be wholly adequate to them as internal intuitions." Not only is no intuition adequate to rational concepts but no concept is adequate to the aesthetic ideas. In any case, the two are closely tied, for "the poet essays the task of interpreting to sense the rational ideas of invisible beings." Of these, he gives two lists: first heaven, hell, eternity, creation (i.e. all religious ideas); and second, things that would fall into the more contemporary category of existential ideas, i.e. death, envy, all vices, love. Now, how is this done? Well, the poet "attempts with the aid of an imagination which emulates the display of reason in the attainment of a maximum": that is, it goes towards the maximum by trying to embody these ideas with a completeness that cannot be found in nature. Poetry, Kant notes, does this best. Then he says, oddly, that the faculty of aesthetic ideas, regarded on its own account, is just a talent of the imagination.
Kant goes further to discuss how the aesthetic ideas not only induce "a wealth of thought as would never admit of comprehension in a definite concept" but that this is also "an unbounded expansion if the concept itself... [and] puts the faculty of intellectual ideas (reason) into motion...towards an extension of thought [that] exceeds what can be laid hold of in that representation or clearly expressed." This does not "constitute the presentation" of the concept itself. Rather, these are "secondary representations" which "express the derivatives" connected with the concept. They also express "kinship with other concepts." That is, they express a certain aura of associated concepts.
Now these forms are "called (aesthetic) attributes." The word "attributes" is not a helpful one for us: much better is "symbol." Aesthetic ideas are, in short, expressed a symbols in works of art, for example Jupiter's eagle as a symbol of Jupiter. They are not defining ("logical") attributes and so, in the case of Jupiter, doe not "represent what lies in our concepts of sublimity and majesty of creation." Rather, they represent "something that gives the imagination an incentive to spread its flight over a whole host of kindred representations that provoke more thought than admits of expression in a concept determined by words."
The aesthetic idea which the symbol furnishes "serves the above rational idea as a substitute for logical presentation" but in this case, its function is to animate the mind, again, by "opening out for it a prospect into a field of kindred representations stretching beyond its ken." Fine art acts in this way not only in painting and sculpture but also in poetry and rhetoric, which also use "attributes" i.e. symbols. These attributes "go hand in hand with the logical" the imagination bringing "more thought into play," though undeveloped, than could be found in the concept or expressible in language.