The Four Books are 'The Great Learning' and 'The Doctrine of the Mean', which came from the 'Classic of Rites', one of the Five Classics, 'The Analects of Confucius', which had been treated as a semi-Classic, and 'The Mengzi', which had ranked with 'The Xunzi'
これは経書の中の『礼記』から分割編纂した「大学」と「中庸」、そして準経書扱いされていた『論語』と、『荀子』と並称されていた『孟子』という四つの書物である。