|Reid’s painting by Henry Raeburn (1796)|
In Section 3, Chapter 1, of the book, Reid looks at the Cogito, ergo sum argument which Descartes has deployed to prove his own existence to himself. Reid asks: “But supposing it proved, that my thought and my consciousness must have a subject, and consequently that I exist, how do I know that all that train and succession of thought which I remember belong to one subject, and that the I of this moment is the very individual I of yesterday and of times past?”
He notes that while Descartes has not addressed this doubt, Locke has done it. Locke’s method of resolving this doubt consists of determining that “personal identity consists in consciousness; that is, if you are conscious that you did such a thing a twelvemonth ago, this consciousness makes you to be the very person that did it. Now, consciousness of what is past can signify nothing else but a remembrance that I did it. So that Locke's principle must be, That identity consists in remembrance ; and consequently a man must lose his personal identity with regard to every thing he forgets.”
He accuses Locke and Hume of fomenting a series of unnecessary doubts which they consistently fail to resolve. Here’s Reid’s take on the role played by skeptic thinkers:
[They] have all employed their genius and skill to prove the existence of a material world; and with very bad success. Poor untaught mortals believe, undoubtedly, that there is a sun, moon, and stars; an earth, which we inhabit; country, friends, and relations, which we enjoy; land, houses, and moveables, which we possess. But philosophers, pitying the credulity of the vulgar, resolve to have no faith but what is founded upon reason. They apply to philosophy to furnish them with reason for the belief of those things which all mankind have believed, without being able to give any reason for it. And surely one would expect, that, in matters of such importance, the proof would not be difficult: but it is the most difficult thing in the world. For these three great men, with the best good will, have not been able, from all the treasures of philosophy, to draw one argument, that is fit to convince a man that can reason, of the existence of any one thing without him.Reid says, “A man that disbelieves his own existence, is surely as unfit to be reasoned with, as a man that believes he is made of glass.” Taken as a whole, Reid’s Inquiry can be seen as an answer to the ideas of the most important philosopher of skepticism, David Hume.