‘By Dr. Blair’s means I have been favoured with the perusal of your performance, which I have read with great pleasure and attention. It is certainly very rare that a piece so deeply philosophical is wrote with so much spirit, and affords so much entertainment to the reader, though I must still regret the disadvantages under which I read it, as I never had the whole performance at once before me, and could not be able to compare one part with another. To this reason chiefly I ascribe some obscurities which, in spite of your short analysis and abstract, seem to hang over your system; for I must do you the justice to own that when I enter into your ideas, no man appears to express himself with greater perspicuity than you do, a talent which above all others is requisite in that species of literature which you have cultivated. There are some objections which I would willingly propose to the chapter “Of Sight,” did I not suspect that they arise from my not sufficiently understanding it. I shall therefore forbear till the whole can lie before me, and shall not at present propose any further difficulties to your reasonings. I shall only say that if you have been able to clear up these abstruse and important subjects, instead of being mortified, I shall be so vain as to pretend to a share of the praise; and shall think that my errors, by having at least some coherence, have led you to make a more strict review of my principles, which were the common ones, and to perceive their futility.’ In his reply to this letter Reid recognises the debt which philosophy owes to the sceptical criticism of Hume. He writes thus to Hume:— ‘KING’S COLLEGE, _18th March 1763_. ‘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.