The work was originally intended as a mere preface to a collected volume of his poems, explaining and justifying his own style and practice in poetry. The work grew to a literary autobiography, including, together with many facts concerning his education and studies and his early literary adventures, an extended criticism of William Wordsworth's theory of poetry as given in the preface to the Lyrical Ballads (a work on which Coleridge collaborated), and a statement of Coleridge's philosophical views. In the first part of the work Coleridge is mainly concerned with showing the evolution of his philosophic creed. At first an adherent of the associational psychology of David Hartley, he came to discard this mechanical system for the belief that the mind is not a passive but an active agency in the apprehension of reality. The author believed in the "self-sufficing power of absolute Genius" and distinguished between genius and talent as between "an egg and an egg-shell". The discussion involves his definition of the imagination or "esemplastic power," the faculty by which the soul perceives the spiritual unity of the universe, as distinguished from the fancy or merely associative function. The book has numerous essays on philosophy. In particular, it discusses and engages the philosophy of Immanuel Kant, Johann Gottlieb Fichte, and Friedrich Wilhelm Joseph von Schelling. Being fluent in German, Coleridge was one of the first major English literary figures to translate and discuss Schelling, in particular. The later chapters of the book deal with the nature of poetry and with the question of diction raised by Wordsworth. While maintaining a general agreement with Wordsworth's point of view, Coleridge elaborately refutes his principle that the language of poetry should be one taken with due exceptions from the mouths of men in real life, and that there can be no essential difference between the language of prose and of metrical composition. A critique on the qualities of Wordsworth's poetry concludes the volume. The book contains Coleridge's celebrated and vexed distinction between "imagination" and "fancy". Chapter XIV is the origin of the famous critical concept of a "willing suspension of disbelief".