Hitoshi Nagai (永井 均, Nagai Hitoshi; born November 10, 1951) is one of the most influential Japanese philosophers, who taught philosophy at Chiba University and later at Nihon University. His main research fields are metaphysics and metaethics. His books include "Philosophy for Kids!" and "A Transfer Student and Black Jack: A Seminar on Solipsity," which interpret solipsism from a unique metaphysical point of view. Nagai's philosophy has been heavily influenced by Wittgenstein, however, his philosophy successfully elucidates an important aspect of solipsism which Wittgenstein could not fully express in his philosophical works. Nagai stresses that the solipsistic subject (such as "I!") can be pointed to by using the public language, but the trial of this pointing ought to be failed every time because of the unique function of our public language. He calls this characteristic "solipsity".