Abstract: According to mainstream studies, the May 4^th Movement is an enlightenment rationality movement. By studying the Science and Philosophy of Life Debate that broke out in 1923, we can find out that there were epistemological dialectics between affect and reason in the debate. The Philosophy of Life School led by Liang Qichao and Cai Yuanpei proposed the theory of philosophia sentimentalis, strongly criticizing scientific rationalism. It maintained that reason and affect were both important, and that affective enlightenment was the key to the problems of life. This was Counter-Enlightenment. The theory of philosophia sentimentalis, intending to break the materialistic-idealistic dichotomy, maintained that affect connected mind and body, life and the universe, subjectivity and objectivity, spirit and matter, while reason was only part of affect. Philosophy of life not only combined with the Aesthetic Education Movement, it also got support from anarchists and Creation Writers while gave support to them, obtaining considerable responses from the intellectual, literary and art circles. The concept of philosophy of life originated from the German word "Lebensanschauung" concocted by Rudolf Eucken in 1890, which was translated into Jinseikan, a kanji neologism invented by Abe Yoshishige in 1912, and then was directly adopted by Chinese intellectuals. Its main focus can be presented as a question: is humans' knowledge about selves, others and the universe derived from affect or reason? Following Henri Bergson and Eucken, the Chinese Philosophy of Life School thought that instead of pursuing pure reason, philosophy should explore the property of life force, which is affect. Affect is not simply feeling or emotion, but the traditional Chinese concept of "qing" that originates from The Book of Changes, and also the affect maintained by Spinoza, Nietzsche, Bergson and Deleuze. The May 4^th Counter-Enlightenment is worthy of our deep research.