Before the Han Dynasty, the character 是 served as a demonstrative pronoun meaning "this." (This usage survives in some idioms and .) Some linguists believe that 是 developed into a copula because it often appeared, as a repetitive subject, after the subject of a sentence (in classical Chinese we can say, for example: "George W. Bush, "this" president of the United States" meaning "George W. Bush "is" the president of the United States). The character 是 appears to be formed as a compound of characters with the meanings of "early" and "straight."