I compare my sensations and notions with those of other men; and if I find a perfect coincidence, I shall then be satisfied that my sensations are according to the law of human nature, and therefore right. To illustrate all this by an example:

I want to know whether my sense of seeing be a well-informed faculty.---First, I have reason to think that it is; because my eyes communicate to me such sensations as I, of my own accord, am disposed to confide in. There is something in my perceptions of sight so distinct, and so definite, that I do not find myself in the least disposed to doubt whether things be what my eyes represent them. Even the obscur er informations of this faculty carry along with them their own evidence, and my belief. I am confident that the sun and moon are round, as they appear to be, that the rainbow is arched, that grass is green, snow white, and the heavens azure; and this I should have believed, though I had passed all my days in solitude, and never known any thing of other animals, or their senses.---Secondly, I find that my notions of the visible qualities of bodies are the same now they have always been. If this were not the case; if where I saw greenness yesterday I were to see yellow to-day, I should be apt to suppose, that my sight had suffered some depravation, except I had reason to think that the object had really changed colour. But indeed we have so strong a tendency to believe our senses, that I doubt not but in such a case I should be more disposed to suspect a change in the object than in my eye-sight: much would depend on the circumstances of the case. We rub our eyes when we want to look at any thing with accuracy; for we know by experience, that motes, and cloudy specks,

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which may be removed by rubbing, do sometimes float in the eye, and hurt the sight. But if the alteration of the visible qualities in the external object be such as we have never experienced from a depravation of the organ, we should be inclined to trust our eye-sight, rather than to suppose that the external object has remained unaltered.---Thirdly, no evil consequence has ever happened to me when acting upon the supposition, that my faculty of seeing is a well informed sense: whereas, if I were to act on the contrary supposition, I should soon have cause to regret my scepticism. I see a post in my way; by turning a little aside, I pass it unhurt: but if I had supposed my sight fallacious, and gone straight forward, a bloody nose, or something worse, might have been the consequence. If, when I bend my course obliquely, in order to avoid the post that seems to stand directly before me, I were to run my head full against it, I should instantly suspect a depravation in my eye-sight: but as I never experience any misfortune of this kind, I believe that my sense of seeing is a well-informed faculty.---Fourthly, the perceptions received by this sense are perfectly consistent with one another, and with the perceptions received by my other faculties. When I see the pearance of a solid body in my way, my touch always confirms the testimony of my sight; if it did not, I should suspect a fallacy in one or other of those senses, perhaps in both. When I look on a line of soldiers, they all seem standing perpendicular, as I myself stand; but if the men at the extremities. of the line, without leaning against any thing, were to appear as if they formed an angle of forty-five degrees with the carth's surface, I should suspect some

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unaccountable obliquity in my vision.-Lastly, after the experience of several years, after all the knowledge I have been able to gather, concerning the sensations of other men, from reading, discourse, and observation, I have no reason to think their sensations of sight different from mine. Every body who uses the English language calls snow white, and grass green; and it would be in the highest degree absurd to suppose, that what they call the sensation of whiteness, is not the same sensation which I call by that name. Some few, perhaps, see differently from me. A man in the jaundice sees that rose yellow which I see red; a short sighted man sees, that picture confusedly at the distance of three yards, which I see distinctly. But far the greater part of mankind see as I do, and differently from those few individuals; whose sense of seeing I therefore consider as less perfect than mine. Nay, though the generality of mankind were short-sighted, still it would be true, that we, who are not so, have the most perfect sight; for our sight is more accurate in its perceptions, qualifies us better for the business of life, and coincides more exactly, or at least more immediately, with the sensations received by the other senses. Yet the short-sighted as well as they who have the acutest sight, trust to this sense, as soon as they are placed in a situation favourable to accurate observation all the difference is, that it is more difficult, and often more inconvenient, for short sighted persons to place themselves in such a situation. Still it should be remembered that a perfect sense and a well informed sense are not synonymous terms. We call a sense well-informed, in opposition to one that is depraved or fallacious. Perfection and imperfection of

sense are relative terms; implying a comparison, either between different men, in respect of the acuteness of their senses and faculties; or between any sense, as it appears in a particular man, and the degree of acuteness which is found to belong to that sense as it appears in the generality of mankind. There are two telescopes, one of which gives a distinct view of an object at two, and the other at four miles distance; both are equally well informed, (if I may so speak); that is, equally true in their representations; but the one is much more imperfect than the other.

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I do not, at présent, offer any further illustrations of these criteria of a well-informed sense. The reader who examines them by the rules of common prudence, will perhaps be satisfied with them at least I am apt to think, that few will suspect the veracity of their faculties when they stand this test. But let it not be supposed, that I mean to insinuate, that a man never trusts his faculties till he first examine them after this manner: we believe our senses previously to all reflection or examination; and we never disbelieve them, but upon the authority of our senses, placed in circumstances more favourable to accurate observation.

If the reader is not satisfied with these criteria, it is no great matter. The question concerning a well-informed sense it is not perhaps easy to answer. I offer these remarks rather as hints to be attended to by other adventurers in this part of science, than as a complete solution of the difficulty. If it were not that I presume some advantage may be derived from them in this way, I should have omitted them alto

gether; for on them does not depend the doctrine I mean to establish.

SECT. III.

The subject continued. Intuitive truths distinguishable

into classes.

F the notions attending the perception of certain truth, we formerly mentioned this as one, "That in regard to such truth, we suppose we should

entertain the same sentiments and belief if we were "perfectly acquainted with all nature *." Lest it should be thought that we mean to extend this notion too far, it seems proper to introduce here the following remarks.

1. The axioms and demonstrated conclusions of geometry are certainly true, and certainly agreeable to the nature of things. Thus we judge of them at present; and thus we necessarily believe, that we should judge of them, even if we were endued with omniscience and infallibility. It is a natural dictate of human understanding, that the contrary of these truths must for ever remain absurd and impossible, and that omnipotence itself cannot change their nature; though it might so deprave our judgment as to make us disbelieve, or not perceive them f.

See part 1. chap. 1.

+ Some authors are of opinion, that all mathematical truth is resolvable into identical propositions. The following remark to this purpose is taken from a Dissertation on Evidence, printed at Berlin in the year 1764. "Omnes mathematicorum propositiones sunt i"denticæ, et repræsentantur hac formula, aa Sunt veritates iden"tice, sub varia forma expressæ, imo ipsum, quod dicitur, contra"dictionis principium, vario modo enunciatum et involutum ; siquidem omnes hujus generis propositiones revera in eo contineantur. Secundum nostram autem intelligendi facultatem ea est propositi