SIR, It is justly observed by Mr. Locke, and by Mr. Hobbes and others before him, that we have no innate ideas, nor can reflect upon them before we have them; that is, we cannot think before we have something to think upon. All objects and materials for thinking must be let in upon the mind through the organs of sense; and when they are there, we reflect or reason upon them; or, to speak philosophically, when the action of exterior bodies strikes upon us, it must cause a second action or motion, and continue it in infinitum, unless it meets obstruction. This first action causes sensation, and the second reflection; and the first seems to me as necessarily to produce the latter, as wind sails a ship, or the winding up of a clock sets it in motion.
Every system of matter has peculiar organizations, and can perform only peculiar functions. A cow cannot perform the offices of a horse, nor a man of a monkey; nor indeed, in many instances, can one man perform those of another. As some machines or systems of matter consist of vastly finer and more numerous parts than others, so they are capable of more operations. A watch which points to minutes or seconds, has more wheels, than one which only shews hours; and a striking or repeating watch has more than both, though all are wound up by the same key. Animals who consist of infinite tubes, veins, arteries, muscles, and juices, which also consist of infinite globular, and other figured particles of matter, must have suitable and very surprizing operations, though all their actions must be confined within the circle of their machine; but they will be multiplied in equal or greater degree than the chances upon dies. Two dies have six times as many chances as one, and three as two, and so on in infinitum; and therefore there seems to be no difficulty in accounting for the great variety of actions in animals, more than in inferior machines: And as mankind never have, nor, I presume, ever will discover all the powers of mechanical experiments; so with greater reason one may venture to assert, that no animal ever yet has exerted all the faculties which it was endued with: A thousand dies may turn up all sixes; but I believe this has never happened, nor I believe ever will.
Vegetables seem to me to be analogous in many respects to animals: Their generation appears to be much alike: They both rise from seeds, or eggs, and continue their kinds by the same: Their life is continued alike, and their nourishment conveyed through veins or other tubes; and when that nourishment ceases, they die; and as the action of the sun, and other bodies, set the former in motion, and causes that sort of sensation which we call vegetation, so the same power, or some other like it, seems to rouze animal life, and sets it in like motion; and all motion must be progressive in the same system till it be destroyed, or that system become another, or part of another; which shall be more fully shewn hereafter.
This action is called by different names, as it affects the different parts of the machine. When it affects the eye, it is called seeing; the ear, hearing; the palate, tasting; the nose, smelling; which indeed are but different sorts of feeling: But when the motion is continued further, and gets to the brain, or other internal parts of the system, it causes that effect which we call thinking; which again operates within the animal, and drives it to farther action, which is always analogous to the disposition of the fabrick, and regular, or irregular, according to the present formation of the machine, and of the powers which impel it. And here we cannot enough admire the exquisite skill of the Supreme Architect, who has formed such stupendous and amazing works of his omnipotence; and in many instances, I conceive we should judge right if we only admired them, and not vainly attempted to find out what we can never know. We want faculties to search the causes of most things in nature, and know nothing of their internal contexture, and but little of the modus of their operations. We see only some sensible effects of the actions of bodies upon one another; but how they produce these effects, we are utterly ignorant, and I believe ever shall be whilst we are in this state: We cannot tell why the fire burns, the grass grows, the eye sees, the ear hears, or the mind thinks, only we find in fact, that they do so; and here is our ne plus ultra.