quire what may be alleged, with greatest appearance of reason, against the proposition we have shewn to be true: for where there is so much prejudice to be encountered, a bare and naked demonstration of the truth will scarce suffice. We must also satisfy the scruples that men may raise in favour of their preconceived notions, shew whence the mistake arises, how it came to spread, and carefully disclose and root out those false persuasions, that an early prejudice might have implanted in the mind.

CXXXIX. First, therefore, it will be demanded, how visible extension and figures come to be called by the same name with tangible extension and figures, if they are not of the same kind with them? It must be something more than humour or accident, that could occasion a custom so constant and universal as this, which has obtained in all ages and nations of the world, and amongst all ranks of men, the learned as well as the illiterate.

CXL. To which I answer, we can no more argue a visible and tangible square to be of the same species, from their being called by the same name, than we can, that a tangible square and the monosyllable consisting of six letters, whereby it is marked, are of the same species, because they are both called by the same name. It is customary to call written words, and the things they signify, by the same name: for words not being regarded in their own nature, or otherwise than as they are marks of things, it had been superfluous, and beside the design of language, to have given them names distinct from those of the things marked by them. The same reason holds here also. Visible figures are the marks of tangible figures, and from sect. lix. it is plain, that in themselves they are little regarded, or upon any other score than for their connexion with tangible figures, which by nature they are ordained to signify. And because this language of nature does not vary in different.

ages or nations, hence it is, that in all times and places visible figures are called by the same names as the respective tangible figures suggested by them, and not. because they are alike, or of the same sort with them.

CXLI. But, say you, surely a tangible square is liker to a visible square than to a visible circle: it has four angles, and as many sides; so also has the visible square, but the visible circle has no such thing, being bounded by one uniform curve, without right lines or angles, which makes it unfit to represent the tangible square, but very fit to represent the tangible circle. Whence it clearly follows, that visible figures are patrons of, or of the same species with, the respective tangible figures represented by them; that they are like unto them, and of their own nature fitted to represent them, as being of the same sort; and that they are in no respect arbitrary signs, as words.

CXLII. I answer, it must be acknowledged, the visible square is fitter than the visible circle to represent the tangible square, but then it is not because it is liker, or more of a species with it; but because the visible square contains in it several distinct parts, whereby to mark the several distinct corresponding parts of a tangible square, whereas the visible circle doth not. The square perceived by touch hath four distinct equal sides, so also hath it four distinct equal angles. It is therefore necessary, that the visible figures which shall be most proper to mark it, contain four distinct equal parts corresponding to the four sides of the tangible square; as likewise four other distinct and equal parts, whereby to denote the four equal angles of the tangible square. And accordingly we see the visible figures contain in them distinct visible parts answering to the distinct tangible parts of the figures signified or suggested by them.

CXLIII. But it will not hence follow, that any visible figure is like unto or of the same species with its corresponding tangible figure, unless it be also shewn,

that not only the number, but also the kind of the parts be the same in both. To illustrate this, I observe that visible figures represent tangible figures, much after the same manner that written words do sounds. Now, in this respect, words are not arbitrary, it not being indifferent what written word stands for any sound; but it is requisite, that each word contain in it so many distinct characters, as there are variations in the sound it stands for. Thus the single letter a is proper to mark one simple uniform sound; and the word adultery is accommodated to represent the sound annexed to it, in the formation whereof, there being eight different collisions, or modifications of the air by the organs of speech, each of which produces a difference of sound, it was fit the word representing it should consist of as many distinct characters, thereby to mark each particular difference, or part of the whole sound: and yet nobody, I presume, will say, the single letter a, or the word adultery, is alike unto, or of the same species with the respective sounds by them represented. It is indeed arbitrary, that in general, letters of any language represent sounds at all; but when that is once agreed, it is not arbitrary what combination of letters shall represent this or that particular sound. I leave this with the reader to pursue, and apply it in his own thought.

CXLIV. It must be confessed that we are not so apt to confound other signs with the things signified, or to think them of the same species, as we are visible and tangible ideas. But a little consideration will shew us how this may be, without our supposing them of a like nature. These signs are constant and universal, their connexion with tangible ideas has been learnt at our first entrance into the world; and ever since, almost every moment of our lives, it has been occurring to our thoughts, and fastening and striking deeper on our minds. When we observe that signs are variable, and of human institution; when we remember, there was a

time they were not connected in our minds with those things they now so readily suggest; but that their signification was learned by the slow steps of experience : this preserves us from confounding them. But when we find the same signs suggest the same things all over the world; when we know they are not of human institution, and cannot remember that we ever learned their signification, but think that at first sight they would have suggested to us the same things they do now: all this persuades us they are of the same species as the things respectively represented by them, and that it is by a natural resemblance they suggest them to our minds.

CXLV. Add to this, that whenever we make a nice survey of any object, successively directing the optic axis to each point thereof; there are certain lines and figures described by the motion of the head or eye, which, being in truth perceived by feeling, do nevertheless so mix themselves, as it were, with the ideas of sight, that we can scarce think but they appertain to that sense. Again, the ideas of sight enter into the mind, several at once more distinct and unmingled, than is usual in the other senses beside the touch. Sounds, for example, perceived at the same instant, are apt to coalesce, if I may so say, into one sound: but we can perceive, at the same time, great variety of visible objects, very separate and distinct from each other. Now tangible extension being made up of several distinct coexistent parts, we may hence gather another reason, that may dispose us to imagine a likeness or analogy between the immediate objects of sight and touch. But nothing, certainly, doth more contribute to blend and confound them together, than the strict and close connexion they have with each other. We cannot open our eyes but the ideas of distance, bodies, and tangible figures, are suggested by them. So swift, and sudden, and unperceived, is the transition from visible to tangible

ideas, that we can scarce forbear thinking them equally the immediate object of vision.

CXLVI. The prejudice, which is grounded on these, and whatever other causes may be assigned thereof, sticks so fast, that it is impossible, without obstinate striving, and labour of the mind, to get entirely clear of it. But then the reluctancy we find, in rejecting any opinion, can be no argument of its truth, to whoever considers what has been already shewn, with regard to the prejudices we entertain concerning the distance, magnitude, and situation, of objects; prejudices so familiar to our minds, so confirmed and inveterate, as they will hardly give way to the clearest demonstration.

CXLVII. Upon the whole, I think, we may fairly conclude, that the proper objects of vision constitute a universal language of the Author of nature, whereby we are instructed how to regulate our actions, in order to attain those things that are necessary to the preservation and well-being of our bodies, as also to avoid whatever may be hurtful and destructive of them. It is by their information that we are principally guided in all transactions and concerns of life. And the manner wherein they signify and mark unto us the objects which are at a distance, is the same with that of languages and signs of human appointment, which do not suggest the things signified, by any likeness or identity of nature, but only by an habitual connexion, that experience has made us to observe between them.

CXLVIII. Suppose one who had always continued blind be told by his guide, that after he has advanced so many steps, he shall come to the brink of a precipice, or be stopped by a wall; must not this, to him, seem very admirable and surprising? He cannot conceive how it is possible for mortals to frame such predictions as these, which, to him, would seem as strange and unaccountable, as prophecy doth to others. Even they who are blessed with the visive faculty, may (though