This chapter argues for the following claims. (1) There is no content that groups the propositions of common sense together. (2) The common-sense grouping has a real purpose: it delineates propositions that we are at a very minimum justified in believing. (3) Common-sense propositions are to be found at the intersection of not-science-based yet widely held beliefs, beliefs not based on testimony or inference, and beliefs whose denials are pragmatically incoherent. (4) Commonsensicality is a graded concept: there are degrees in which propositions are propositions of common sense. (5) Propositions of common sense are objects of at least one of the following attitudes: belief, disposition to believe, or taking for granted in the sense of presupposing them, either as a justification-conferring presupposition or as a pragmatic presupposition. (6) Although we can give up common-sense propositions, we should only do so in the face of very weighty evidence.

This introduction shows why and how common sense matters to philosophy, thus lighting up the terrain that subsequent chapters explore in much greater detail. First, it explains briefly what common sense is, and next, what common-sense philosophy is. Then it considers whether, and if so, how, common sense should matter to philosophy; can we not do without common sense? Subsequently, it turns to criticisms of the idea that common sense matters to philosophy, and of the very idea of common-sense philosophy. It concludes with a short note on the organization of the book.

History can be a fickle judge. After enjoying enormous popularity in the United States, Great Britain, and France for almost one hundred years after his death, Thomas Reid (1710-96) disappeared from the philosophical canon. Reid's disappearance did not have the consequence that his thought failed to influence subsequent philosophers: One can discern, for example, distinctly Reidian themes and methodology at work in Moorean “ordinary language” philosophy. But it did mean that Reid made no appearance in the story that philosophers in the last century have told - and continue to tell - about the development of early modern philosophy. The basic shape of this story is familiar enough and goes something like this:I

Early modern philosophy was animated by two central worries: First, given its dismal history of disagreement and present state of faction, how could philosophy progress in the way and to the degree that the natural sciences had? And, second, how could traditional objects of philosophical inquiry such as free will, the soul, and God be fit into the world as described by the new science? The urgency of both these issues occasioned a crisis in modern philosophy. In their own way, and with varying degrees of success, rationalists such as Descartes and empiricists such as Hume grappled with these issues. But only in the figure of Immanuel Kant do we encounter a sustained and ingenious attempt to blend the rationalist and empiricist ways of addressing these problems.

This essay is a discussion of Reid's views on memory and the identity of persons through time. These topics are closely related, although there has been, and still is, a serious controversy about the exact nature of the relation. John Locke, on the one hand, made the case for what has come to be called the “Memory Theory of Personal Identity,” according to which the identity of persons through time is constituted by the memory that a person has of his or her past actions, experiences, and so forth. Thomas Reid, on the other hand, thought this was absurd, and argued for the thesis that the relation between memory and identity is simply of an evidential nature: Memory gives a person evidence that he or she is the same person as the person who did, or experienced some thing at some previous time.

The first section is a discussion of Reid’s views regarding memory as a source of knowledge, while the second considers his views on personal identity through time. In both sections, I will pay special attention to two features of Reid’s thought. The first feature is that there are, as Reid says, things that are “obvious and certain” with respect to memory and personal identity. Unlike Descartes, Reid doesn’t start by methodically doubting everything that seems obvious and certain. Rather, he endorses the principle that what seems obvious and certain is innocent until proven guilty. That is, what seems obvious and certain may legitimately be accepted as a starting point for philosophical reflection until it is shown that such acceptance is irrational, unjustified, or unwarranted. This endorsement is at least part of what makes Reid a common sense philosopher.