It was under these conditions that the letters of eminent men in the eighteenth century and the early part of the nineteenth century were generally written. In the former century letter-writing was undoubtedly a recognised form of high literary workmanship, with close affinities on one side to the diary or private journal, and on another to the essay. Long, continuous, and intimate correspondence, as in the case of Swift and Walpole, gravitated toward the journal; dissertations on literature, politics, and manners were more akin to the essay; while in the hands of the novelist the journalistic series of letters took artificial development into a method of story-telling. On the other side, the tendency of epistles to become essays reached its climax in the letters of Burke, some of which are only distinguishable from brilliant pamphlets by the formal address and subscription.
With the nineteenth century begins an era of amusing and animated letter-writing. The classic and somewhat elaborate style of the preceding age falls into disuse; the essayist draws gradually back into a department of his own; the new school reflects, as is natural, the general tendency of English literature toward a livelier and more varied movement, with a wider range of subjects and sympathies. In his letters, as in his poetry, the precursor of the Naturalistic school was Cowper, who could be simple without being trivial, was never prosy and often pathetic, and who possessed the rare art of stamping on his reader's mind an enduring impression of quiet and somewhat commonplace society in the English midlands. That poets should usually have been good letter-writers is probably no more than might have been expected, for imagination and word-power must tell everywhere; yet the list is so long as to be worth noticing. Swift, Pope, Gray, and Cowper in the last century, and in the present century Scott, Byron, Shelley, Coleridge, and Southey, have all left us distinctive and copious correspondence. Wordsworth may, perhaps, be classed as a notable exception; for Wordsworth's letters are dull, being at their best more like essays or literary dissertations than the free outpouring of intimate thought. They have none of the charm which comes from the revelation of private doubt or passionate affection that is ordinarily stifled by convention; they are, on the contrary, eminently respectable, deliberate, and carefully expressed. 'It has ever been the habit of my mind,' he writes, 'to trust that expediency will come out of fidelity to principles, rather than to seek my principles of action in calculations of expediency.' This is what the Americans call 'high toned'; but the metal is too heavy for the light calibre of a letter.