Barfield's Poetic Diction opens with examples of "felt changes" arising in reading poetry, and discusses how these relate to general principles of poetic composition. But Barfield's greater agenda is "a study of meaning". Using poetic examples, he attempts to demonstrate how the imagination works with words and metaphors to create meaning. He shows how the imagination of the poet creates new meaning, and how this same process has been active, throughout human experience, to create and continuously expand language. For Barfield this is not just literary criticism: it is evidence for the evolution of human consciousness. This, for many readers, is his real accomplishment: his unique presentation of "not merely a theory of poetic diction, but a theory of poetry, and not merely a theory of poetry, but a theory of knowledge". This theory was developed directly from a close study of the evolution of words and meaning, starting with the relation between the primitive mind's myth making capacity, and the formation of words. Barfield uses numerous examples to demonstrate that words originally had a unified "concrete and undivided" meaning, which we now distinguish as several distinct concepts. For example, the single Greek word pneuma (which can be variously translated as "breath", "spirit", or "wind") reflects, Barfield argues, the primordial unity of these concepts of air, spirit, wind, and breath, all included in one "holophrase". This Barfield considers not the application of analogy to natural phenomena, but the discernment of its pre-existence. This is the perspective Barfield believes is original in the evolution of consciousness, which was "fighting for its life", as he phrases it, in the philosophy of Plato, and which, in a regenerate and more sophisticated form, benefiting from the development of rational thought, needs to be recovered if consciousness is to continue to evolve.