The first theory of self-knowledge we will consider is the acquaintance theory. According to the acquaintance theory, we have direct, unmediated access to some of our mental states because we stand in the metaphysical relation of acquaintance to them. Our acquaintance with mental states allows introspective self-knowledge to be especially secure, epistemically. In particular, it allows self-knowledge to be more secure than perceptual knowledge, since perception provides only indirect access to its objects. The acquaintance theory is most famously associated with Bertrand

Russell, who gave it this name. But some philosophers before Russell, including Descartes, accepted the acquaintance theory’s core idea that introspective knowledge is peculiarly direct and therefore especially secure. More importantly for our purposes, some contemporary philosophers base their own theories of self-knowledge on this core idea. These contemporary theories can reasonably be regarded as versions of the acquaintance theory. They will be our main focus.1