The Cloud of Unknowing, ed. by Evelyn Underhill, , at sacred-texts.com
Of the first secondary power, Imagination by name; and of the works and the obedience of it unto Reason, before Sin and after.
IMAGINATION is a power through the which we portray all images of absent and present things, and both it and the thing that it worketh in be contained in the Memory. Before ere man sinned, was Imagination so obedient unto the Reason, to the which it is as it were servant, that it ministered never to it any unordained image of any bodily creature, or any fantasy of any ghostly creature: but now it is not so. For unless it be refrained by the light of grace in the Reason, else it will never cease, sleeping or waking, for to portray p. 281 diverse unordained images of bodily creatures; or else some fantasy, the which is nought else but a bodily conceit of a ghostly thing, or else a ghostly conceit of a bodily thing. And this is evermore feigned and false, and next unto error.
This inobedience of the Imagination may clearly be conceived in them that be newlings turned from the world unto devotion, in the time of their prayer. For before the time be, that the Imagination be in great part refrained by the light of grace in the Reason, as it is in continual meditation of ghostly things—as be their own wretchedness, the passion and the kindness of our Lord God, with many such other—they may in nowise put away the wonderful and the diverse thoughts, fantasies, and images, the which be ministered and printed in their mind by the light of the curiosity of Imagination. And all this inobedience is the pain of the original sin. p. 282