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sion by means of that which was made upon the organ; and probably, by means of the nerves, some impression must be made upon the brain. Fourthly, The impression made upon the organ, nerves, and brain, is followed by a sensation. And, last of all, This sensation is followed by the perception of the object.
Thus our perception of objects is the result of a train of operations ; some of which affect the body only, others affect the mind. We know very little of the nature of some of these operations; we know not at all how they are connected together, or in what way they contribute to that perception which is the result of the whole : but, by the laws of our constitution, we perceive objects in this, and in no other way.
What perception is, every one will know better by reflecting on what he does himself, what he sees, hears, feels, &c. or thinks, thạn by any discourse of another. Whoever reflects on what passes in his own mind, cannot miss it : and if he does not reflect, all the words in the world can. not make him have any notion of it.
III. Perceptions are of two kinds.
Our perceptions are of two kinds ; some are natural and original, others acquired, and the fruit of experience. When we perceive that this is the taste of cider, that of brandy ; and this is the smell of an apple, that of an orange; that this is the noise of thunder, that the ringing of bells : this the sound of a coach passing, that the voice of such a friend ; these perceptions, and others of the same kind, are not original, they are acquired. But the perception which we have by touch, of the hardness and softness of bodies, of their extension, figure and motion, is not acquired; it is original.
In all our senses, the acquired perceptions are many more than the original, especially in sight. By this sense we perceive originally the visible figure and colour of bodies only, and their visible place; but we learn to perceive by the eye almost every thing which we can perceive by touch. The original perceptions of this sense, serve only as signs to introduce the acquired.
The signs by which objects are presented to us in perception, are the language of nature to man; and as, in many respects, it hath great affinity with the language of man to man ; so particularly in this, that both are partly natural and original, partly acquired by custom. Our original or natural perceptions are analogous to the natural language of man to man; and our acquired perceptions are analogous to artificial language, which in our mother tongue, is got very much in the same manner with our acquired perceptions, as we shall afterwards more fully explain.
Not only men, but children, idiots, and brutes, acquire by habit many perceptions which they had not originally. Almost every employment in life, hath perceptions of this kind that are peculiar to it. The shepherd knows every sheep of his flock, as we do our acquaintance, and can pick them out of another flock one by one. The butcher knows by sight the weight and quality of his beeves and sheep before they are killed. The farmer perceives by his eye, very nearly, the quantity of hay in a rick, or of corn in a heap. The sailor sees the burden, the build, and the distance of a ship at sea, while she is a great way off.—Every man accustomed to writing, distinguishes his acquaintance by their hand writing, as he does by their faces. And the painter distinguishes in the works of his art, the style of all the great masters. In a word, acquired perception is very different in different persons, according to the diversity of objects about which they are employed, and the application they bestow in observing them.
- There is no reasoning in perception, as hath been observed. The belief which is implied in it, is the effect of instinct. But there are many things, with regard to sensible objects, which we can infer from what we perceive; and such conclusions of reason ought to be distinguished from what is merely perceived. When we look at the moon, we perceive her to be sometimes circular, sometimes horned, and sometimes gibbous. This is simple perception, and is the same in the philosopher and the clown : but from these various appearances of her enlightened part, it is to be inferred that she is really of a spherical figure. This conclusion is not obtained by simple perception, but by reasoning. Simple perception has the same relation to the conclusions of reason drawn from our perceptions, as the axioms in mathematics have to the propositions. We cannot demonstrate that two quantities, which are equal to the same quantity are equal to each other ; neither can we demonstrate, that the tree, which we perceive, exists. But, by the constitution of our nature, our belief is irresistibly carried along by our apprehension of the axiom ; and by the constitution of our nature, our belief is no less irresistibly carried along by our perception of the tree. All reasoning is from principles. The first principles of mathematical reasoning are mathematical axioms and definitions ; and the first principles of all our reasoning about existence, are our perceptions. The first principles of every kind of reasoning are given us by nature, and are of equal authority with the faculty of reason itself, which is also the gift of nature. The conclusions of reason are built upon first principles, and can have no other foundation.
When a long train of reasoning is necessary in demonstrating a mathematical proposition, it is easily distinguished from an axiom, and they seem to be things of a very different nature. But there are some propositions which lie so near to axioms, that it is difficult to say, whether they ought to be held as axioms, or demonstrated as propositions. The same thing holds with regard to perception, and the conclusions drawn from it. Some of these conclusions follow our perceptions so easily, and are so immediately connected with them, that it is difficult to fix the limit which divides the one from the other.
Perception, whether original or acquired, implies no exercise of reason ; and is common to men, children, idiots and brutes. The more obvious conclusions drawn from our perceptions, by reason, make what we call common understanding ; by which men conduct themselves in the common affairs of life, and by which they are distinguished from idiots. The more remote conclusions which are drawn from our perceptions by reason, make what we commonly call science, in the various parts of nature, whether in agriculture, medicine, mechanics, or in any part of natural philosophy. When we see a garden in good order, containing a great variety of things of the best kinds, and in the most flourishing condition, we immediately conclude from these signs, the skill and industry of the gardener. A farmer when he rises in the morning, and perceives that the neighbouring brook overflows his fields, concludes that a great deal of rain hath fallen in the night. Perceiving his fence broken and his corn trode den down, he concludes that some of his own or his neighbour's cattle have broke loose. Perceiving that his stabledoor is broken open and some of his horses gone, he concludes that a thief has carried them off. He traces the prints of his horses' feet in the soft ground, and by them discovers which road the thief hath taken. These are instances of common understanding, which dwells so near to perception, that it is difficult to trace the line which divides the one from the other. In like manner, the science of nature dwells so near to common understanding, that we cannot discern where the latter ends and the former begins. We perceive that bodies lighter than water swim in water, and that those which are heavier sink. Hence, we conclude, that if a body remains wherever it is put under water, whether at the top or bottom, it is precisely of the same weight with the water. If it will rest only when part of it is above water, it is lighter than water. And the greater the part above water is, compared with the whole, the lighter is the body. If it had no gravity at all, it would make no impression upon the water, but stand wholly above it. Thus, every man, by common understanding, has a rule by which he judges of the specific gravity of bodies which swim in water : and a step or two more leads him into the science of hydrostatics.
All that we know of nature or of existences, may be compared to a tree, which hath its root, trunk, and branches. In this tree of knowledge, perception is the root, common understanding is the trunk, and the sciences are the branches.
IV. Perception the inlet of Knowledge.
Perception then being the first step and degree towards knowledge, and the inlet of all the materials of it, the fewer senses any man, as well as any other creature, hath, and the fewer and duller the impressions are that are made by them, and the duller the faculties are employed about them, the more remote are they from that knowledge which is to be found in some men. But this being in a great variety of degrees, (as may be perceived among men) cannot certainly be discovered in the several species of animals, much less in their particular individuals. It suffices only to remark here, that perception is the first operation of all our intellectual faculties, and the inlet of all knowledge in our minds.