I find it very hard to persuade several that their passions are affected by words from whence they have no ideas; and yet harder to convince them that in the ordinary course of conversation we are sufficiently understood without raising any images of the things concerning which we speak. It seems to be an odd subject of dispute with any man, whether he has ideas in his mind or not. Of this, at first view, every man, in his own forum, ought to judge without appeal. But, strange as it may appear, we are often at a loss to know what ideas we have of things, or whether we have any ideas at all upon some subjects. It even requires a good deal of attention to be thoroughly satisfied on this head. Since I wrote these papers, I found two very striking instances of the possibility there is, that a man may hear words without having any idea of the things which they represent, and yet afterwards be capable of returning them to others, combined in a new way, and with great propriety, energy, and instruction. The first instance is that of Mr. Blacklock, a poet blind from his birth. Few men blessed with the most perfect sight can describe visual objects with more spirit and justness than this blind man; which cannot possibly be attributed to his having a clearer conception of the things he describes than is common to other persons. Mr. Spence, in an elegant preface which he has written to the works of this poet, reasons very ingeniously, and, I imagine, for the most part, very rightly, upon the cause of this extraordinary phenomenon; but I cannot altogether agree with him, that some improprieties in language and thought, which occur in these poems, have arisen from the blind poet's imperfect conception of visual objects, since such improprieties, and much greater, may be found in writers even of a higher class than Mr. Blacklock, and who, notwithstanding, possessed the faculty of seeing in its full perfection. Here is a poet doubtless as much affected by his own descriptions as any that reads them can be; and yet he is affected with this strong enthusiasm by things of which he neither has, nor can possibly have, any idea further than that of a bare sound: and why may not those who read his works be affected in the same manner that he was; with as little of any real ideas of the things described? The second instance is of Mr. Saunderson, professor of mathematics in the University of Cambridge. This learned man had acquired great knowledge in natural philosophy, in astronomy, and whatever sciences depend upon mathematical skill. What was the most extraordinary and the most to my purpose, he gave excellent lectures upon light and colors; and this man taught others the theory of those ideas which they had, and which he himself undoubtedly had not. But it is probable that the words red, blue, green, answered to him as well as the ideas of the colors themselves; for the ideas of greater or lesser degrees of refrangibility