After teaching at a high school in Tianjin for a year, Yu returned to Peking University to pursue graduate studies in philosophy.
[1] During the Hundred Flowers Campaign of 1957, Yu wrote four letters that advocated rationalism, democracy and freedom, and socialist rule of law.
[1] During his two-decade-long banishment from academia, Yu focused on self-study of Xuanxue, the philosophy of China's Six Dynasties period (third to sixth centuries), an era of division and turmoil.
In his autobiography, he reminisced that he found solace in the ancient philosophers' reflections on fate, and their pursuit of freedom of thought and self-awareness in the face of adversity.
[1] After the end of the Cultural Revolution, Yu returned to academia in 1978 and became a researcher at the Institute of World Religions of the Chinese Academy of Social Sciences.