1. As standing water put into motion by the stroke of a stone, or blast of wind, doth not presently give over moving as soon as the wind ceaseth, or the stone settleth: so neither doth the effect cease which the object hath wrought upon the brain, so soon as ever by turning aside of the organ the object ceaseth to work; that is to say, though the sense be past, the image or conception remaineth; but more obscurely while we are awake, because some object or other continually plieth and soliciteth our eyes, and ears, keeping the mind in a stronger motion, whereby the weaker doth not easily appear. And this obscure conception is that we call PHANTASY or IMAGINATION: imagination being (to define it) conception remaining, and by little and little decaying from and after the act of sense.
2. But when present sense is not, as in SLEEP, there the images remaining after sense (when there be any) as in dreams, are not obscure, but strong and clear, as in sense itself. The reason. iS, because that which obscured and made the conceptions weak, namely sense, and present operation of the objects, is removed. For sleep is the privation of the act of sense, (the power remaining) and dreams are the imaginations of them that sleep.
3. The causes of DREAMS (if they be natural) are the actions or violence of the inward parts of a man upon his brain, by which the passages of sense, by sleep benumbed, are restored to their motion. The signs by which this appeareth to be so, are the differences of dreams proceeding from the different accidents of man's body. Old men being commonly less healthful and less free from inward pains, are thereby more subject to dreams, especially such dreams as be painful: as dreams of lust, or dreams of anger, according as the heart, or other parts within, work more or less upon the brain, by more or less heat. So also the descent of different sorts of phlegm maketh one to dream of different tastes of meats or drinks. And I believe there is a reciprocation of motion from the brain to the vital parts, and back from the vital parts to the brain; whereby not only imagination begetteth motion in those parts; but also motion in those parts begetteth imagination like to that by which it was begotten. If this be true, and that sad imaginations nourish the spleen, then we see also a cause, why a strong spleen reciprocally causeth fearful dreams. And why the effects of lasciviousness may in a dream produce the image of some person that hath caused them. If it were well observed, whether the image of the person in a dream be as obedient to the accidental heat of him that dreameth, as waking his heat is to the person, and if so, then is such motion reciprocal. Another sign that dreams are caused by the action of the inward parts, is the disorder and casual consequence of one conception or image to another: for when we are waking, the antecedent thought or conception introduceth, and is cause of the consequent, as the water followeth a man's finger upon a dry and level table. But in dreams there is commonly no coherence (and when there is, it is by chance), which must proceed from this, that the brain in dreams is not restored to its motion in every part alike; whereby it cometh to pass, that our thoughts appear like the stars between the flying clouds, not in the order which a man would choose to observe them in, but as the uncertain flight of broken clouds permit.
4. As when the water, or any liquid thing moved at once by divers movements, receiveth one motion compounded of them all; so also the brain or spirits therein, having been stirred by divers objects, composeth an imagination of divers conceptions that appeared. singly to the sense. As for example, the sense sheweth us at one time the figure of a mountain, and at another time the colour of gold; but the imagination afterwards hath them both at once in a golden mountain. From the same cause it is, there appear unto us castles in the air, chimeras, and other monsters which are not in rerum natura, but have been conceived by the sense in pieces at several times. And this composition is that which we commonly call FICTION of the mind.
