The problem of the existence or nonexistence of certain Chinese characters in ancient times has not been solved till now. Based on the theory of judging from the futures of linguistic materials， this paper takes the character “xin”(信) in oracle bone inscriptions and bronze inscriptions in the West Zhou Dynasty as an example so as to put forward a new approach： an exhausted search can tell us the answer in the context that can fully reflect the existence of characters in a certain time and requires a compulsive appearance of relative characters. Since we can figure out the contexts in oracle bone inscriptions and bronze inscriptions in the West Zhou Dynasty where the character “xin” shall appear， and such contexts belong to heated topics in which “xin” must appear if it exists， the fact that the character “xin” is not in extant oracle bone inscriptions and bronze inscriptions in the West Zhou Dynasty means that “xin” did not exist in the writing system in the Shang and West Zhou Dynasties.