Zeami mixed a variety of Classical and Modern themes in his writing, and made use of Japanese and Chinese traditions. He incorporated numerous themes of Zen Buddhism into his works and later commentators have debated the extent of his personal interest in Zen. The exact number of plays that he wrote is unknown, but is likely to be between 30 and 50. He wrote many treatises about Noh, discussing the philosophy of performance. These treatises are the oldest known works on the philosophy of drama in Japanese literature, but did not see popular circulation until the 20th-century.