The earliest writing in China is the oracle bone inscriptions of the Shang Dynasty, which records early Chinese, also known as oracle bone Chinese, which are all monosyllabic-words (1300 BC). In the Bronze Inscriptions of the Western Zhou Dynasty and later handed down documents, doublets appear (beginning in 1046 BC). At present, the philological academy believes that the doublets recorded with two Chinese single-characters come from reduplication of two single-character symbols, but there is no complete argument and reliable evidence. This article, by using the opposite method of argument, reversely assumes that the single-characters (monosyllabic words) come from doublets and tries to demonstrate it. The article proves the truth of the origin of doublets based on the word distribution and semantic correspondence between doublets and single-characters in “the Book of Poetry”, that is, doublets are the source and single-characters are flows. Among them, 39.66% of the doublets have no corresponding single-characters, and they are the characters created to record doublets; 41.92% of the meanings of doublets have nothing to do with the meanings of single-characters, which proves that the doublets does not come from the combination of single-characters; 12.46% of the meanings of doublets are interpreted as the meanings of single-characters, which are the subjective errors of later generations of interpreters; the remaining 5.66% are only associated with proclitics and enclitics rather than single-characters. Finally, the article proposes that doublets originate from a unique mechanism of expressive morphology, which is a new type of etymological theory outside the morphological grammar system, and can create various polysyllabic ideophones, including the onomatopoeia or mimetic words. The article proves that a language begins with the creation of words. In the prehistoric period before the oracle bone inscriptions, Chinese ancestors had invented a large number of distinctive doublets (AA), couplets (AB) and other polysyllabic words (xA, or ABB, ABA’B), or ideophones. Due to the difficulty of writing, the doublets were hidden in spoken language for hundreds of years. It was not until the time of “Book of Poetry” and “Book of History” in the bronze inscriptions of the Western Zhou Dynasty that it entered the history and has continued to this day. Doublets are the earliest Chinese words and the beginning of Chinese civilization.