“It has been observed before that images, however beautiful, though faithfully copied from nature, and as accurately represented in words, do not of themselves characterize the poet. They become proofs of original genius only as far as they are modified by a predominant passion; or by associated thoughts or images awakened by that passion; or when they have the effect of reducing multitude to unity, or succession to an instant; or lastly, when a human and intellectual life is transferred to them from the poet's spirit.”

Vol. 2 "On Philosophy and the Intellect" as translated in Essays and Aphorisms (1970), as translated by R. J. Hollingdale
Parerga and Paralipomena (1851), Counsels and Maxims
Context: The poet presents the imagination with images from life and human characters and situations, sets them all in motion and leaves it to the beholder to let these images take his thoughts as far as his mental powers will permit. This is why he is able to engage men of the most differing capabilities, indeed fools and sages together. The philosopher, on the other hand, presents not life itself but the finished thoughts which he has abstracted from it and then demands that the reader should think precisely as, and precisely as far as, he himself thinks. That is why his public is so small.

Source: 1950s, The Image: Knowledge in Life and Society, 1956, p. 25

Source: Rhetoric as Philosophy (1980), p. 32

Thomas Gray "Some Remarks on the Poems of Lydgate", in The Works of Thomas Gray (1858) vol. 5, pp. 308-9.
Criticism

as quoted by Ilya Prigogine in his Autobiography http://nobelprize.org/nobel_prizes/chemistry/laureates/1977/prigogine-autobio.html given at the occasion of Prigogine's 1977 Nobel Prize in Chemistry.

Preface of M. Quetelet
A Treatise on Man and the Development of His Faculties (1842)
Context: The principal artists of the era of the revival of letters, such as Leon Baptista Alberti, Michael Angelo, Leonardo da Vinci, Albert Durer, with many others who what art ought to borrow from science, felt the necessity of resorting to observation, in order to rebuild in some sort the ruined monument of ancient artistical skill. They studied nature in a philosophical manner; sought to strike out the limits within which they ought to confine themselves in order to be truthlike... and from those profound studies which kept them ever before the face of nature, they deduced original views and new models, destined to distinguish for ever that celebrated age. The proportions of the human body did not alone attract their attention: anatomy, perspective, and chemistry, formed parts of their studies; nothing was neglected; and some of these great artists even gained for themselves a first place among the geometers of their day. Their successors have not devoted themselves to such serious studies, and hence it so frequently happens that they are reduced to content themselves, either with copying from those who went before them, or with working after individual models, whose proportions they modify according to mere caprice, without having any just or proper ideas of the beautiful.

Source: Dialogues II

"Le monde où l'on catche," in Mythologies (1957)

"Poetry: A Few Don'ts by an Imagist", Poetry: A Magazine of Verse (March 1913)