The decay of sense in men waking is not the decay of the motion made in sense, but an obscuring of it in such manner as the light of the sun obscureth the light of the stars, which stars do no less exercise their virtue by which they are visible, in the day than in the night. But because amongst many strokes which our eyes, ears, and other organs receive from external bodies, the predominant only is sensible; therefore the light of the sun being predominant, we are not affected with the action of the stars. And any object being removed from our eyes, though the impression it made in us remain, yet other objects more present succeeding and working on us, the imagination of the past is obscured and made weak, as the voice of a man is in the noise of the day. From whence it followeth that the longer the time is, after the sight or sense of any object, the weaker is the imagination. For the continual change of man's body destroys in time the parts which in sense were moved; so that distance of time, and of place, hath one and the same effect in us. For as at a great distance of place that which we look at appears dim and without distinction of the smaller parts, and as voices grow weak and inarticulate, so also after great distance of time our imagination of the past is weak; and we lose, for example, of cities we have seen, many particular streets; and of actions, many particular circumstances. This decaying sense, when we would express the thing itself, I mean fancy itself, we call imagination, as I said before. But when we would express the decay, and signify that the sense is fading, old, and past, it is called memory. So that imagination and memory are but one thing, which for diverse considerations hath diverse names.

The imaginations of them that sleep are those we call "dreams". And these also, as all other imaginations, have been before, either totally or by parcels, in the sense. And, because in sense, the brain and nerves, which are the necessary organs of sense, are so benumbed in sleep as not easily to be moved by the action of external objects, there can happen in sleep no imagination, and therefore no dream, but what proceeds from the agitation of the inward parts of man's body; which inward parts, for the connexion they have with the brain and other organs, when they be distempered, do keep the same in motion; whereby the imaginations there formerly made, appear as if a man were waking; saving that the organs of sense being now benumbed, so as there is no new object which can master and obscure them with a more vigorous impression, a dream must needs be more clear in this silence of sense than are our waking thoughts. And hence it cometh to pass that it is a hard matter, and by many thought impossible, to distinguish exactly between sense and dreaming. For my part, when I consider that in dreams I do not often nor constantly think of the same persons, places, objects, and actions, that I do waking, nor remember so long a train of coherent thoughts, dreaming, as at other times, and because waking I often observe the absurdity of dreams, but never dream of the absurdities of my waking thoughts, I am well satisfied that, being awake, I know I dream not, though when I dream, I think myself awake.

The most difficult discerning of a man's dream from his waking thoughts is, then, when by some accident we observe not that we have slept: which is easy to happen to a man full of fearful thoughts, and whose conscience is much troubled, and that sleepeth without the circumstances of going to bed or putting off his clothes, as one that noddeth in a chair. For he that taketh pains, and industriously lays himself to sleep, in case any uncouth and exorbitant fancy come unto him, cannot easily think it other than a dream. We read of Marcus Brutus (one that had his life given him by Julius Caesar, and was also his favorite, and notwithstanding murdered him), how at Philippi, the night before he gave battle to Augustus Caesar, he saw a fearful apparition, which is commonly related by historians as a vision, but, considering the circumstances, one may easily judge to have been but a short dream. For sitting in his tent, pensive and troubled with the horror of his rash act, it was not hard for him, slumbering in the cold, to dream of that which most affrighted him; which fear, as by degrees it made him wake, so also it must needs make the apparition by degrees to vanish; and, having no assurance that he slept, he could have no cause to think it a dream or anything but a vision. And this is no very rare accident; for even they that be perfectly awake, if they be timorous and superstitious, possessed with fearful tales, and alone in the dark, are subject to the like fancies, and believe they see spirits and dead men's ghosts walking in churchyards; whereas it is either their fancy only, or else the knavery of such persons as make use of such superstitious fear to pass disguised in the night to places they would not be known to haunt.

From this ignorance of how to distinguish dreams and other strong fancies from vision and sense, did arise the greatest part of the religion of the Gentiles in time past, that worshipped satyrs, fauns, nymphs, and the like; and nowadays the opinion that rude people have of fairies, ghosts, and goblins, and of the power of witches. For, as for witches, I think not that their witchcraft is any real power, but yet that they are justly punished for the false belief they have that they can do such mischief, joined with their purpose to do it if they can; their trade being nearer to a new religion than to a craft or science. And for fairies and walking ghosts, the opinion of them has, I think, been on purpose either taught, or not confuted, to keep in credit the use of exorcism, of crosses, of holy water, and other such inventions of ghostly men. Nevertheless there is no doubt but God can make unnatural apparitions; but that He does it so often as men need to fear such things more than they fear the stay, or change of the course of Nature, which He also can stay and change, is no point of Christian faith. But evil men, under pretext that God can do anything, are so bold as to say anything when it serves their turn, though they think it untrue; it is the part of a wise man to believe them no further than right reason makes that which they say appear credible. If this superstitious fear of spirits were taken away, and with it prognostics from dreams, false prophecies, and many other things depending thereon, by which crafty ambitious persons abuse the simple people, men would be would be much more fitted than they are for civil obedience.

And this ought to be the work of the schools; but they rather nourish such doctrine. For, not knowing what imagination, or the senses are, what they receive, they teach: some saying that imaginations rise of themselves, and have no cause; others that they rise most commonly from the will, and that good thoughts are blown (inspired) into a man by God, and evil thoughts by the devil; or that good thoughts are poured (infused) into a man by God, and evil ones by the devil. Some say the senses receive the species of things, and deliver them to the common sense, and the common sense delivers them over to the fancy, and the fancy to the memory, and the memory to the judgement, like handing of things from one to another, with many words making nothing understood.

The imagination that is raised in man, or any other creature endued with the faculty of imagining by words or other voluntary signs, is that we generally call "understanding", and is common to man and beast. For a dog by custom will understand the call or the rating of his master; and so will many other beasts. That understanding which is peculiar to man is the understanding not only his will but his conceptions and thoughts, by the sequel and contexture of the names of things into affirmations, negations, and other forms of speech; and of this kind of understanding I shall speak hereafter.