Sec. 29. A most important thing, therefore, in the perception of form is the formation of types in our mind, with reference to which examples are to be judged. I say the formation of them, for we can hardly consider the theory that they are eternal as a possible one in psychology. The Platonic doctrine on that point is a striking illustration of an equivocation we mentioned in the beginning;[7] namely, that the import of an experience is regarded as a manifestation of its cause -- the product of a faculty substituted for the description of its function. Eternal types are the instrument of aesthetic life, not its foundation. Take the aesthetic attitude, and you have for the moment an eternal idea; an idea, I mean, that you treat as an absolute standard, just as when you take the perceptive attitude you have an external object which you treat as an absolute existence. But the aesthetic, like the perceptive faculty, can be made an object of study in turn, and its theory can be sought; and then the eternal idea, like the external object, is seen to be a product of human nature, a symbol of experience, and an instrument of thought. The question whether there are not, in external nature or in the mind of God, objects and eternal types, is indeed not settled, it is not even touched by this inquiry; but it is indirectly shown to be futile, because such transcendent realities, if they exist, can have nothing to do with our ideas of them. The Platonic idea of a tree may exist; how should I deny it? How should I deny that I might some day find myself outside the sky gazing at it, and feeling that I, with my mental vision, am beholding the plenitude of arboreal beauty, perceived in this world only as a vague essence haunting the multiplicity of finite trees? But what can that have to do with my actual sense of what a tree should be? Shall we take the Platonic myth literally, and say the idea is a memory of the tree I have already seen in heaven? How else establish any relation between that eternal object and the type in my mind? But why, in that case, this infinite variability of ideal trees? Was the Tree Beautiful an oak, or a cedar, an English or an American elm? My actual types are finite and mutually exclusive; that heavenly type must be one and infinite. The problem is hopeless.