Perhaps Wimsatt's most influential theories come from the essays "The Intentional Fallacy" and "The Affective Fallacy" (both are published in Verbal Icon) which he wrote with Monroe Beardsley.
Wimsatt and Beardsley argue that the effect of poetic language alone is an unreliable way to analyze poetry because, they contend, words have no effect in and of themselves, independent of their meaning.