Reid tells us that his rejection of “the common theory of ideas” is the centerpiece of his reply to skepticism. He often writes, in fact, as if rejecting that theory is by itself sufficient to answer the skeptical arguments of Berkeley, Hume, and others. In this essay I will argue that Reid's reply to skepticism is more complex than Reid himself portrays it. While Reid's rejection of the theory of ideas clearly plays a central role in his reply to skepticism, it seems to me that this is only one important element of his reply, and not one that is sufficient to do the job all by itself. On the contrary, Reid's reply to the skeptic depends also on (a) Reid's own theory of perception, (b) his theory of evidence, and (c) an important aspect of Reid's methodology. In the sections that follow, I will discuss each of these elements of Reid's philosophy in turn. In addition to explicating Reid, I will also be defending him. That is, I will argue that, taken together, these four elements of Reid's philosophy constitute a successful reply to the skeptic.

I. REID'S REJECTION OF THE THEORY OF IDEAS

According to Reid, the theory of ideas is both necessary and sufficient for generating sweeping skeptical results. This means that any successful reply to skepticism requires rejecting the theory of ideas. In this section of the essay, I consider what Reid means by “the common theory of ideas,” and why he thinks the theory is so closely connected with skepticism. I also review some of Reid’s reasons for rejecting the theory.