This paper hypothesizes that, since Japanese has a special word for private self, but not for public self, various words are used to represent the latter. Conversely, English has a special word for public self, but lacks such a special word for private self, so that personal pronouns are used to represent the private self. This hypothesis allows a principled account of marked differences between these two languages. For example, it explains why the Japanese system of personal pronouns does not correspond directly to that of English.