In addition, although some articles of "Nihonshoki" were cited from other books, their titles were not usually clear and only phrases such as 'a book says,' 'another book says' or 'an old book says' were written.
なお、『日本書紀』では既存の書物から記事を引用する場合「一書曰」、「一書云」、「一本云」、「別本云」、「旧本云」、「或本云」などと書名を明らかにしないことが多い。