SIR,--On Monday last, Mr. John Farquhar brought me your letter of February 25th, enclosed in one from Dr. Blair. I thought myself very happy in having the means of obtaining at second-hand, through the friendship of Dr. Blair, your opinion of my performance: and you have been pleased to communicate it directly in so polite and friendly a manner, as merits great acknowledgments on my part. Your keeping a watchful eye over my style, with a view to be of use to me, is an instance of candour and generosity to an antagonist, which would affect me very sensibly, although I had no personal concern in it, and I shall always be proud to follow so amiable an example. Your judgment of the style, indeed, gives me great consolation, as I was very diffident of myself in regard to English, and have been indebted to Drs. Campbell and Gerard for many corrections of that kind. In attempting to throw some new light upon these abstruse subjects, I wish to preserve the due mean betwixt confidence and despair. But whether I have any success in this attempt or not, I shall always avow myself your disciple in metaphysics. I have learned more from your writings in this kind, than from all others put together. Your system appears to me not only coherent in all its parts, but likewise justly deduced from principles commonly received among philosophers; principles which I never thought of calling in question, until the conclusions you draw from them in the "Treatise of Human Nature" made me suspect them. If these principles are solid, your system must stand; and whether they are or not, can better be judged after you have brought to light the whole system that grows out of them, than when the greater part of it was wrapped up in clouds and darkness. I agree with you, therefore, that if this system shall ever be demolished, you have a just claim to a great share of the praise, both because you have made it a distinct and determinate mark to be aimed at, and have furnished proper artillery for the purpose.