Imagination
Imagination is generally held to be the power of forming mental images or other concepts not directly derived from sensation. In spite of the popular usage of the term, the majority of philosophers from Aristotle to Immanuel Kant considered it in relation to knowledge or opinion. They conceived it either as an element in knowledge or as an obstacle to it—as in Plato's attack on art—or as both an obstacle and an element. David Hume is a representative of the last view: "Nothing is more dangerous to reason than flights of the imagination, and nothing has been the occasion of more mistakes among philosophers." Yet in the same place he wrote of the understanding as "the general and more established properties of the imagination" (Treatise of Human Nature, Book I, Part IV, Sec. vii). The fancy, the power of the imagination to combine ideas in fantastical ways, is to be avoided, but nevertheless imagination is vital to knowledge.
This latter element in Hume's view had its greatest development in Kant's Critique of Pure Reason, where the imagination is described as a "blind but indispensable function of the soul, without which we should have no knowledge whatsoever, but of which we are scarcely ever conscious." Kant thought that the imagination has two tasks to perform in giving rise to knowledge, though it is not always easy to separate them.
