The roots of Taoism go back at least to the 4th century BCE. Early Taoism drew its cosmological notions from the School of Yinyang (Naturalists) and was deeply influenced by one of the oldest texts of Chinese culture, the "I Ching" ("Yi Jing"), which expounds a philosophical system about how to keep human behaviour in accordance with the alternating cycles of nature. The "Legalist" Shen Buhai (c. 400 – c. 337 BCE) may also have been a major influence, expounding a realpolitik of "wu wei".