Coleridge was fully aware of a special power, both of imagination and of verse-music, in the poem. His attempts to complete it in 1800 brought persistently to his mind the project of a philosophy of poetry, and especially of this poem, as we may infer from a letter to Poole in March, 1801: "I shall ... immediately publish my 'Christabel,' with two essays annexed to it, on the 'Preternatural' and on 'Metre.'" When the two cantos were at last printed in 1816, Coleridge wrote in the Preface: "The metre of the 'Christabel' is not, properly speaking, irregular, though it may seem so from its being founded on a new principle: namely, that of counting in each line the accents, not the syllables. Though the latter may vary from seven to twelve, yet in each line the accents will be found to be only four. Nevertheless this occasional variation in number of syllables is not introduced wantonly, or for the mere ends of convenience, but in correspondence with some transition, in the nature of the imagery or passion." This is not to be taken quite literally. The accentual principle was assuredly nothing new in English verse, and syllable-counting, though introduced by Chaucer, had to be reintroduced by the Renaissance poets and did not become an unquestioned convention till the latter part of the seventeenth century. But the return to free accentual verse in the "Christabel" was an innovation at the beginning of the nineteenth century. It is to be noted, too, that there are lines of three and even of two accents in Part I. In chap. XV. of the _Biographia Literaria_, in a list of the "specific symptoms of poetic power" in Shakespeare's early work, Coleridge places first "the perfect sweetness of the versification; its adaptation to the subject; and the power displayed in varying the march of the words.... The sense of musical delight, with the power of producing it, is a gift of imagination; and this, together with the power of reducing multitude into unity of effect, and modifying a series of thoughts by some one predominant thought or feeling, may be cultivated and improved, but can never be learnt. It is in these that _Poeta nascitur non fit_."