I understand self-knowledge as any kind of knowledge about one's own mental states, which also includes knowledge about the truth of one's own beliefs. In the first part of my talk, I will illustrate that we can acquire self-knowledge from two different perspectives, firstly from an ordinary first-person-perspective and, secondly, from a detached point of view, which I call first-person-knowledge from a third-person-perspective.
In the second part, I will apply the introduced notions to the problem of external world skepticism. I will argue that the problem results from shifting the perspectives on our own mental states. From the ordinary perspective, we can know that the skeptical hypothesis is false, but from a third-person-perspective, we cannot. By distinguishing between two perspectives, we can achieve a solution to the skeptical problem as well as an explanation of its apparent plausibility.