3. On the other side, if reasoning aright I win not consent (which may very easily happen) from them that being confident of their own knowledge weigh not what is said, the fault is not mine but theirs. For as it is my part to show my reasons, so it is theirs to bring attention.
4. Man's nature is the sum of his natural faculties and powers, as the faculties of nutrition, motion, generation, sense, reason, &c. For these powers we do unanimously call natural, and are contained in the definition of man, under these words, animal and rational.
5. According to the two principal parts of man, I divide his faculties into two sorts, faculties of the body, and faculties of the mind.
6. Since the minute and distinct anatomy of the powers of the body is nothing necessary to the present purpose, I will only sum them up into these three heads, power nutritive, power motive, and power generative.
7. Of the powers of the mind there be two sorts, cognitive or imaginative or conceptive; and motive. And first of the cognitive.
8. For the understanding of what I mean by the power cognitive, we must remember and acknowledge that there be in our minds continually certain images or conceptions of the things without us, insomuch that if a man could be alive, and all the rest of the world annihilated, he should nevertheless retain the image thereof, and of all those things which he had before seen and perceived in it; every man by his own experience knowing that the absence or destruction of things once imagined, doth not cause the absence or destruction of the imagination itself. This imagery and representations of the qualities of things without us is that we call our cognition, imagination, ideas, notice, conception, or knowledge of them. And the faculty, or power, by which we are capable of such knowledge, is that I here call power cognitive, or conceptive, the power of knowing or conceiving.
Chapter 2: The Cause of Sense
1. Having declared what I mean by the word conception, and other words equivalent thereunto, I come to the conceptions themselves, to show their difference, their causes, and the manner of their production as far as is necessary for this place.
2. Originally all conceptions proceed from the actions of the thing itself, whereof it is the conception. Now when the action is present, the conception it produceth is called SENSE, and the thing by whose action the same is produced is called the OBJECT of sense.
3. By our several organs we have several conceptions of several qualities in the objects; for by sight we have a conception or image composed of colour or figure, which is all the notice and knowledge the object imparteth to us of its nature by the eye. By hearing we have a conception called sound, which is all the knowledge we have of the quality of the object from the ear. And so the rest of the senses also are conceptions of several qualities, or natures of their objects.
4. Because the image in vision consisting in colour and shape is the knowledge we have of the qualities of the object of that sense; it is no hard matter for a man to fall into this opinion, that the same colour and shape are the very qualities themselves; and for the same cause, that sound and noise are the qualities of the bell, or of the air. And this opinion hath been so long received, that the contrary must needs appear a great paradox; and yet the introduction of species visible and intelligible (which is necessary for the maintenance of that opinion) passing to and fro from the object, is worse than any paradox, as being a plain impossibility. I shall therefore endeavour to make plain these four points:
(1) That the subject wherein colour and image are inherent, is not the object or thing seen.
(2) That that is nothing without us really which we call an image or colour.
(3) That the said image or colour is but an apparition unto us of that motion, agitation, or alteration, which the object worketh in the brain or spirits, or some internal substance of the head.
(4) That as in conception by vision, so also in the conceptions that arise from other senses, the subject of their inherence is not the object, but the sentient.
5. Every man hath so much experience as to have seen the sun and other visible objects by reJection in the water and in glasses, and this alone is sufficient for this conclusion: that colour and image may be there where the thing seen is not. But because it may be said that notwithstanding the image in the water be not in the object, but a thing merely phantastical, yet there may be colour really in the thing itself; I will urge further this experience: that divers times men see directly the same object double, as two candles for one, which may happen by distemper, or otherwise without distemper if a man will, the organs being either in their right temper, or equally distempered. The colours and figures in two such images of the same thing cannot be inherent both therein, because the thing seen cannot be in two places: one of these images thereof is not inherent in the object. But seeing the organs of sight are then in equal temper or equal distemper, the one of them is no more inherent than the other, and consequently neither of them both are in the object; which is the first proposition mentioned in the precedent section.
6. Secondly, that the image of any thing seen by reJection in glass or water or the like, is not any thing in or behind the glass, or in or under the water, every man may prove to himself; which is the second proposition.
7. For the third, we are to consider first, that upon every great agitation or concussion of the brain, as it happeneth from a stroke, especially if the stroke be upon the eye, whereby the optic nerve suffereth any great violence, there appeareth before the eyes a certain light, which light is nothing without, but an apparition only, all that is real being the concussion or motion of the parts of that nerve. From which experience we may conclude, that apparition of light without, is really nothing but motion within. If therefore from lucid bodies there can be derived motion, so as to affect the optic nerve in such manner as is proper thereunto, there will follow an image of light somewhere in that line by which the motion was last derived unto the eye; that is to say, in the object, if we look directly on it, and in the glass or water, when we look upon it in the line of reJection, which in effect is the third proposition, namely, That image and colour is but an apparition unto us of that motion, agitation, or alteration, which the object worketh in the brain, or spirits, or some internal substance in the head.
8. But that from all lucid, shining and illuminated bodies, there is a motion produced to the eye, and, through the eye, to the optic nerve, and so into the brain, by which that apparition of light or colour is effected, is not hard to prove. And first, it is evident that the fire, the only lucid body here on earth, worketh by motion equally every way; insomuch as the motion thereof stopped or inclosed, it is presently extinguished, and no more fire. And farther, that that motion, whereby the fire worketh, is dilatation, and contraction of itself alternately, commonly called scintillation or glowing, is manifest also by experience. From such motion in the fire must needs arise a rejection or casting from itself of that part of the medium which is contiguous to it, whereby that part also rejecteth the next, and so successively one part beateth back the other to the very eye; and in the same manner the exterior part of the eye (the laws of refraction still observed) presseth the interior. Now the interior coat of the eye is nothing else but a piece of the optic nerve, and therefore the motion is still continued thereby into the brain, and by resistance or reaction of the brain, is also a rebound in the optic nerve again, which we not conceiving as motion or rebound from within, think it is without, and call it light; as hath been already shewed by the experience of a stroke. We have no reason to doubt, that the fountain of light, the sun, worketh any other wise than the fire, at least in this matter, and thus all vision hath its original from such motion as is here described. For where there is no light, there is no sight; and therefore colour also must be the same thing with light, as being the effect of lucid bodies: their difference being only this, that when the light cometh directly from the fountain to the eye, or indirectly by reflection from clean and polite bodies, and such as have no particular motion internal to alter it, we call it light. But when it cometh to the eyes by reflection from uneven, rough, and coarse bodies,