Secondly the best philosphy (the deserved title of the Cartesian) derives all sensitive perception from motion, and corporal impress; some account of which we have above given. Not that the formality of it consists in material reaction, as Master Hobbes affirms, totally excluding any immaterial concurrence: but that the representations of objects to the soul, the only animadversive principle, are conveyed by motions made upon the immediate instruments of sense. So that the diversity of our sensations ariseth from the diversity of the motion or figure of the object; which in a different manner affect the brain, whence the soul hath its immediate intelligence of the quality of what is presented. Thus the different effects, which fire and water, have on us, which we call heat and cold, result from the so differing configuration and agitation of their particles; and not from, I know not what chimerical beings, supposed to inhere in the objects, their cause, and thence to be propagated by many petty imaginary productions to the seat of sense. So that what we term heat and cold, and other qualities, are not properly according to philosophical rigour in the bodies, their efficients: but are rather names expressing our passions; and therefore not strictly attributable to anything without us, but by extrinsic denominations, as vision to the wall.
This I conceive to be an hypothesis, well worthy a rational belief: and yet is it so abhorrent from the vulgar, that they would as soon believe Anaxagoras, that snow is black, as him that should affirm, it is not white; and if any should in earnest assert, that the fire is not formally hot, it would be thought that the heat of his brain had fitted him for Anticyra, and that his head were so to madness: for it is conceived to be as certain, as our faculties can make it, that the same qualities, which we resent within us, are in the object, their source. And yet this confidence is grounded on no better foundation, than a delusory prejudice, and the vote of misapplied sensations, which have no warrant to determine either one or other. I may indeed conclude, that I am formally hot or cold; I feel it. But whether these qualities are formally, or only eminently in their producent; is beyond the knowledge of the sensitive. Even the Peripatetic philosophy will teach us, that heat is not in the body of the sun, but only virtually, and as in its cause; though it be the fountain and great distributor of warmth to the neather creation: and yet none urge the evidence of sense to disprove it: neither can it with any more justice be alleged against this hypothesis. For if it be so as Descartes would have it; yet sense would constantly present it to us, as now. We should feel heat as constantly from fire; it would increase in the same degrees, in our approach, and we should find the same excess within the flame: which yet I think to be the chief inducements to the adverse belief: for fire (I retain the instance, which yet may be applied to other cases) being constant in its specifical motions in those smaller derivations of it, which are its instruments of action, and therefore in the same manner striking the sentient, though gradually varying according to the proportions of more or less quantity or agitation, &c. will not fail to produce the same effect in us, which we call heat, when ever we are within the orb of its activity. So that the heat must needs be augmented by proximity, and most of all within the Flame, because of the more violent motion of the particles there, which therefore begets in us a stronger sentiment. Now if this motive energy, the instrument of this active element, must be called heat; let it be so, I contend not. I know not how otherwise to call it: to impose names is part of the People's Charter, and I fight not with words, only I would not that the idea of our passions should be applied to anything without us, when it hath its subject nowhere but in ourselves. This is the grand deceit, which my design is to detect, and if possible, to rectify.
We have seen then two notorious instances of sensitive deception, which justify the charge of Petron. Arbiter.
Fallunt nos oculi, vagiq; sensus
oppressa ratione mentiuntur.
And yet to speak properly, and to do our senses right, simply they are not deceived, but only administer an occasion to our forward understandings to deceive themselves: and so though they are some way accessory to our delusion; yet the more principal faculties are the capital offenders. If the senses represent the Earth as art and immoveable; they give us the truth of their sentiments. To sense, it is so, and it would be deceit to present it otherwise. For (as we have shown) though it do move in itself; it rests to us, who are carried with it. And it must needs be to sense unalterably quiescent, in that our own rotation prevents the variety of successive impress; which only renders motion sensible. And so if we erroneously attribute our particular incommnunicable sensations to things, which do no more resemble them than the effect doth its equivocal cause; our senses are not in fault, but our precipitate judgments. We feel such, or such a sentiment within us, and herein is no cheat or misprision: 'tis truly so, and our sense concludes nothing of its rise or origin. But if hence our understandings falsly deduct, that there is the same quality in the external impressor; 'tis it is criminal, our sense is innocent. When the ear tingles, we really hear a sound: if we judge it without us, it's the fallacy of our judgments. The apparitions of our frighted fancies are real sensibles: but if we translate them without the compass of our brains, and apprehend them as external objects; it's the unwary rashness of our understanding deludes us. And if our disaffected palates resent nought but bitterness from our choicest viands, we truly taste the unpleasing quality, though falsly conceive it in that, which is no more than the occasion of its production. If any find fault with the novelty of the notion; the learned St. Austin stands ready to confute the charge: and they who revere antiquity, will derive satisfaction from so venerable a suffrage. He tells us, si quis remum frangi in aqua opinatur, &, cum aufertur, integrari; non malum habet internuncium, sed malus est judex. And onward to this purpose, the sense could not otherwise perceive it in the water, neither ought it: for since the water is one thing, and the air another; 'tis requisite and necessary, that the sense should be as different as the medium: wherefore the eye sees aright; if there be a mistake; 'tis the judgment's the deceiver. Elsewhere he saith, that our eyes misinform us not, but faithfully transmit their resentment to the mind. And against the Sceptics, that it's a piece of injustice to complain of our senses, and to exact from them an account, which is beyond the sphere of their notice: and resolutely determines, quicquid possunt videre oculi, verum vident. So that what we have said of the senses' deceptions, is rigidly to be charged only on our careless understandings, misleading us through the ill management of sensible informations. But because such are commonly known by the name of the senses deceits (somewhat the more justifiably in that they administer the occasion) I have thought good to retain the usual way of speaking, though somewhat varying from the manner of apprehending.