But when...

But when, from the observations we have made of divers particulars, we make a general idea to represent any species in general, as man; or else join several ideas together, which we never observed to exist together, we call it imagination. So that memory is always the picture of something, the idea whereof has existed before in our thoughts, as near the life as we can draw it; but imagination is a picture drawn in our minds without reference to a pattern.

And here it may be observed that the ideas of memory, like painting after the life, come always short, i. e. want something of the original. For whether a man would remember the dreams he had in the night, or the sights of a foregoing day, some of the traces are always left out, some of the circumstances are forgotten; and those kind of pictures, like those represented successively by several looking-glasses, are the more dim and fainter the further they are off from the original object.

For the mind, endeavouring to retain only the traces of the pattern, losing by degrees a great part of them, and not having the liberty to supply any new colours or touches of its own, the picture in the memory every day fades and grows dimmer, and oftentimes is quite lost.

But the imagination, not being tied to any pattern, but adding what colours, what ideas it pleases, to its own workmanship, making originals of its own which are usually very bright and clear in the mind, and sometimes to that degree that they make impressions as strong and as sensible as those ideas which come immediately by the senses from external objects,-so that the mind takes one for the other, and its own imagination for realities.

And in this, it seems, madness consists, and not in the want of reason; for allowing their imagination to be right, one may observe that madmen usually reason right from them: and I guess that those who are about madmen, will find that they make very little use of their memory, which is to recollect particulars past with their circumstances: but having any particular idea suggested to their memory, fancy dresses it up after its own fashion, without regard to the original.

Hence also one may see how it comes to pass that those that think long and intently upon one thing, come at last to have their minds disturbed about it, and to be a little cracked as to that particular.