Self-consciousness is the source or set of information about our own present mental states. My self-knowledge is the set of all my information about myself, not only about my present mental states, but also my past mental states, my personality, my body or even my unconsciousness. Many philosophers thought that self-consciousness data are certain knowledge (Brentano, Husserl, Ingarden) but many contemporary philosophers claim that the first-person knowledge does not exist (Wittgenstein, Ryle, Dennett). Davidson refutes both behaviorism and subjectivity myth and takes some moderate position: first-person knowledge is dependent on third-person knowledge but third-person knowledge is dependent on first-person knowledge. There are some problems to reduce consciousness to physical states and to know about it. So, first-person knowledge is not certain and autonomous but it does exist and play important role. The two interdependent kinds of knowledge are two pillars of human knowledge. According to Davidson there is also some third pillar and it is the second-person knowledge.