The 'Essay on Man' was intended to have been comprised in four books:—

The first of which, the author has given us under that title, in four epistles.

The second was to have consisted of the same number:—1. Of the extent and limits of human reason. 2. Of those arts and sciences, and of the parts of them, which are useful, and therefore attainable, together with those which are unuseful, and therefore unattainable. 3. Of the nature, ends, use, and application of the different capacities of men. 4. Of the use of learning, of the science of the world, and of wit; concluding with a satire against the misapplication of them, illustrated by pictures, characters, and examples.

The third book regarded civil regimen, or the science of politics, in which the several forms of a republic were to have been examined and explained; together with the several modes of religious worship, as far forth as they affect society; between which the author always supposed there was the most interesting relation and closest connexion; so that this part would have treated of civil and religious society in their full extent.

The fourth and last book concerned private ethics or practical morality, considered in all the circumstances, orders, professions, and stations of human life.

The scheme of all this had been maturely digested, and communicated to the Lord Bolingbroke, Dr Swift, and one or two more, and was intended for the only work of his riper years; but was, partly through ill health, partly through discouragements from the depravity of the times, and partly on prudential and other considerations, interrupted, postponed, and, lastly, in a manner laid aside.

But as this was the author's favourite work, which more exactly reflected the image of his strong capacious mind, and as we can have but a very imperfect idea of it from the disjecta membra poetae that now remain, it may not be amiss to be a little more particular concerning each of these projected books. The first, as it treats of man in the abstract, and considers him in general under every one of his relations, becomes the foundation, and furnishes out the subjects, of the three following; so that—

The second book takes up again the first and second epistles of the first book, and treats of man in his intellectual capacity at large, as has been explained above. Of this, only a small part of the conclusion (which, as we said, was to have contained a satire against the misapplication of wit and learning) may be found in the fourth book of 'The Dunciad,' and up and down, occasionally, in the other three.

The third book, in like manner, reassumes the subject of the third epistle of the first, which treats of man in his social, political, and religious capacity. But this part the poet afterwards conceived might be best executed in an epic poem; as the action would make it more animated, and the fable less invidious; in which all the great principles of true and false governments and religions should be chiefly delivered in feigned examples.

The fourth and last book pursues the subject of the fourth epistle of the first, and treats of ethics, or practical morality; and would have consisted of many members; of which the four following epistles were detached portions: the two first, on the characters of men and women, being the introductory part of this concluding book.—Warburton.