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quickly becomes familiar, and is what chiefly fits us for the use of language. Indeed, in the extent of this capacity, as much, perhaps, as in anything, lies also the principal natural superiority of one man over another.
But, that we may be satisfied that to this kind of reasoning, in its earliest and simplest form, little or no reflection is necessary, let it be observed, that it is now universally admitted by opticians, that it is not purely from sight, but from sight aided by experience, that we derive our notions of the distance of visible objects from the eye. The sensation, say they, is instantaneously followed by a conclusion or judgment founded on experience. The point is determined from the different phases of the object, found, in former trials, to be connected with different distances, or from the effort that accompanies the different conformations we are obliged to give the organs of sight, in order to obtain a distinct vision of the object. Now if this be the case, as I think hath been sufficiently evinced of late, it is manifest that this judgment is so truly instantaneous, and so perfectly the result of feeling and association, that the forming of it totally escapes our notice. Perhaps in no period of life will you find a person that, on the first mention of it, can be easily persuaded that he derives this knowledge from experience. Every man will be ready to tell you that he needs no other witnesses than his eyes to satisfy him that objects are not in contact with his body, but are at different distances from him, as well as from one another. So passive is the mind in this matter, and so rapid are the transitions which, by this ideal attraction, she is impelled to make, that she is, in a manner, unconscious of her own operations. There is some ground to think, from the exact analogy which their organs bear to ours, that the discovery of distance from the eye is attained by brutes in the same manner as by us. As to this, however, I will not be positive. But though, in this way, the mind acquires an early perception of the most obvious and necessary truths, without which the bodily organs would be of little use, in matters less important, her procedure is much slower, and more the result of voluntary application; and as the exertion is more deliberate, she is more conscious of her own activity, or, at least, remembers it longer. It is, then, only that in common style we honour her operation with the name of reasoning ; though there is no essential difference between the two cases. It is true, indeed, that the conclusions in the first way, by which also in infancy we learn language, are commonly more to be regarded as infallible, than those effected in the second.
Part III. The Subdivisions of Moral Reasoning. But to return to the proposed distribution of moral evi.
dence. Under it I include these three tribes, experience, analogy, and testimony. To these I shall subjoin the consideration of a fourth, totally distinct from them all, but which appears to be a mixture of the demonstrative and the moral, or, rather, a particular application of the former, for ascertaining the precise force of the latter. The evidence I mean is that resulting from calculations concerning chances.
I. Erperience. The first of these I have named peculiarly the evidence of experience, not with philosophical propriety, but in compliance with common language, and for distinction's sake. Analogical reasoning is surely reasoning from a more indirect experience. Now as to this first kind, our experience is either uniform or various. In the one case, provided the facts on which it is founded be sufficiently numerous, conclusion is said to be morally certain. In the other, the conclusion built on the greater number of instances is said to be probable, and more or less so, according to the proportion which the instances on that side bear to those on the opposite. Thus, we are perfectly assured that iron thrown into the river will sink, that deal will float, because these conclusions are built on a full and uniform experience. That in the last week of December next it will snow in any part of Britain specified, is perhaps probable; that is, is, on inquiry or recollection, we are satisfied that this hath more frequently happened than the contrary; that some time in that month it will snow is more probable, but not certain, because, though this conclusion be founded on experience, that experience is not uniform; lastly, that it will snow some time during winter, will, I believe, on the same principles, be pronounced certain.
It was affirmed that experience, or the tendency of the mind to associate ideas under the notion of causes, effects, or adjuncts, is never contradicted by one example only. This assertion, it may be thought, is contradicted by the principle on which physiologists commonly proceed, who consider one accurate experiment in support of a particular doctrine as sufficient evidence. The better to explain this phenomenon, and the farther to illustrate the nature of experience, I shall make the following observations: First, whereas sense and memory are conversant only about individuals, our earliest experiences imply, or perhaps generate, the notion of a species, including all those individuals which have the most obvious and universal resemblance. From Charles, Thomas, William, we ascend to the idea of man; from Britain, France, Spain, to the idea of kingdom. As our acquaintance with nature enlarges, we discover resemblances of a striking and important nature, between one species and another, which naturally begets the notion of a genus. From comparing
men with beasts, birds, fishes, and reptiles, we perceive that they are all alike possessed of life, or a principle of sensation and action, and of an organized body, and hence acquire the idea of animal; in like manner, from comparing kingdoms with republics and aristocracies, we obtain the idea of nation, and thence, again, rise in the same track to ideas still more comprehensive. Farther, let it be remembered, that by experience we not only decide concerning the future from the past, but concerning things uncommon from things familiar, which resemble them.
Now to apply this observation: A botanist, in traversing the fields, lights on a particular plant, which appears to be of a species he is not acquainted with. The flower, he observes, is monopetalous, and the number of flowers it carries is seven. Here are two facts that occur to his observation ; let us consider in what way he will be disposed to argue from them. From the first he does not hesitate to conclude, not only as probable, but as certain, that this individual, and all of the same species, invariably produce monopetalous flowers. From the second, he by no means concludes, as either certain or even probable, that the flowers which either this plant, or others of the same species, carry at once, will always be
This difference, to a superficial inquirer, might seem capricious, since there appears to be one example, and but one in either case, on which the conclusion can be founded. The truth is, that it is not from this example only that he deduces these inferences. Had he never heretofore taken the smallest notice of any plant, he could not have reasoned at all from these remarks. The mind recurs instantly from the unknown to all the other known species of the same genus, and thence to all the known genera of the same order or tribe; and having experienced in the one instance a regularity in every species, genus, and tribe, which admits no exception; in the other, a variety as boundless as is that of season, soil, and culture, it learns hence to mark the difference.
Again, we may observe that, on a closer acquaintance with those objects wherewith we are surrounded, we come to discover that they are mostly of a compound nature, and that not only as containing a complication of those qualities called accidents, as gravity, mobility, colour, extension, figure, solidity, which are common almost to all matter, not only as consisting of different members, but as comprehending a mixture of bodies, often very different in their nature and properties, as air, fire, water, earth, salt, oil, spirit, and the like. These, perhaps, on deeper researches, will be found to consist of materials still simpler. Moreover, as we advance in the study of nature, we daily find more reason to be convinced of her constancy in all her operations, that like causes in ljke circumstances always produce like effects, and inverse
ly, like effects always flow from like causes. The inconstancy which appears at first in some of Nature's works, a more improved experience teacheth us to account for in this
As most of the objects we know are of a complex nature, on a narrow scrutiny we find that the effects ascribed to them ought often solely to be ascribed to one or more of the component parts; that the other parts no way contribute to the production; that, on the contrary, they sometimes tend to hinder it. If the parts in the composition of similar objects were always in equal quantity, their being compounded would make no odds; if the parts, though not equal, bore always the same proportion to the whole, this would make a difference, but such as in many cases might be computed. In both respects, however, there is an immense variety. Perhaps every individual differs from every other individual of the same species, both in the quantities and in the proportions of its constituent members and component parts. This diversity is also founded in other things, which, though hardly reducible to species, are generally known by the same name. The atmosphere in the same place at different times, or at the same time in different places, differs in density, heat, humidity, and the number, quality, and proportion of the vapours or particles with which it is loaden. "The more, then, we become acquainted with elementary natures, the more we are ascertained by a general experience of the uniformity of their operations. And though, perhaps, it be impossible for us to attain the knowledge of the simplest elements of any body, yet, when anything appears so simple, or, rather, so exactly uniform, as that we have observed it invariably to produce similar effects, on discovering any new effect, though but by one experiment, we conclude, from the general experience of the efficient, a like constancy in this energy as in the rest. Fire consumes wood, melts copper, and hardens clay. In these instances it acts uniformly, but not in these only. I have always experienced hitherto, that whatever of any species is consumed by it at once, all of the same species it will consume upon trial at any time. The like may be said of what is melted, or hardened, or otherwise altered by it. If, then, for the first time, I try the influence of fire on any fossil, or other substance, whatever be the effect, I readily conclude that fire will always produce a similar effect on similar bodies. This conclusion is not founded on this single instance, but on this instance compared with a general experience of the regularity of this element in all its operations.
So much for the first tribe, the evidence of experience, on which I have enlarged the more, as it is, if not the foundation, at least the criterion, of all moral reasoning whatever. It is, besides, the principal organ of truth in all the branches
of physiology (I use the word in its largest acceptation), including natural history, astronomy, geography, mechanics, optics, hydrostatics, meteorology, medicine, chemistry. Under the general term I also comprehend natural theology and psychology, which, in my opinion, have been most unnaturally disjoined by philosophers. Spirit, which here comprises only the Supreme Being and the human soul, is surely as much included under the notion of natural object as a body is, and is knowable to the philosopher purely in the same way, by observation and experience.
II. Analogy. The eviaence of analogy, as was hinted above, is but a more indirect experience, founded on some remote similitude. As things, however, are often more easily comprehended by the aid of example than by definition, I shall in that manner illustrate the difference between experimental evidence and analogical. The circulation of the blood in one human body is, I shall suppose, experimentally discovered. Nobody will doubt of this being a sufficient proof, from experience, that the blood circulates in every human body. Nay, farther, when we consider the great similarity which other animal bodies bear to the human body, and that both in the structure and in the destination of the several organs and limbs ; particularly when we consider the resemblance in the blood it. self, and bloodvessels, and in the fabric and pulsation of the heart and arteries, it will appear sufficient experimental evidence of the circulation of the blood in brutes, especially in quadrupeds. Yet, in this application, it is manifest that the evidence is weaker than in the former. But should I from the same experiment infer the circulation of the sap in vegetables, this would be called an argument only from analogy: Now all reasonings from experience are obviously weakened in proportion to the remoteness of the resemblance subsisting between that on which the argument is founded, and that concerning which we form the conclusion.
The same thing may be considered in a different way. I have learned from experience that like effects sometimes pro. ceed from objects which faintly resemble, but not near so frequently as from objects which have a more perfect likeness. By this experience, I am enabled to determine the degrees of probability from the degrees of similarity, in the different cases.
It is presumable that the former of these ways has the earliest influence, when the mind, unaccustomed to reflection, forms but a weak association, and, consequently, but a weak expectation of a similar event from a weak resemblance. The latter seems more the result of thought, and is better adapted to the ordinary forms of reasoning.
It is allowed that analogical evidence is at best but a feeblo