"The essential feature of his theory, which he sees as separating it from the others, is its commitment to the proposition that the mind through concentrated study and discipline can apprehend some degree of truth about human experience and can then express that truth in poetic language which realizes it both emotionally and intellectually. He also sees that the effect of such apprehension and expression is not just intellectual, but also moral: the mind is enabled not only to recognize in truth what a particular good is, but also to define, and then avoid, those things that would interfere with the realization of the good in question. The value of poetry is that it achieves this end in a more inclusive manner than philosophical or scientific discourse by utilising both aspects of language, the connotative and the denotative, and by appealing to and engaging both the emotional and the intellectual faculties of the human being."
(A long chain of links to reach this: Here, the author (a dissertation by John Martin Finlay, University of Albama) summarises the Foreword of Yvor Winters' In Defense of Reason)