The military enlightenment occurred along with the Enlightenment has been overlooked for a long time. The debate between enlightenment and anti-enlightenment in the military field at that time formed the intellectual background and starting point of Clausewitz's war discourse. Both sides of the debate useda structural metaphor to answer "What is war?". The affirmative side applied the metaphor of "clock" to stress that there were laws for war and material force played a dominant role in war. On the contrary, the opposition side used the metaphor of "drama" to highlight contingency and spiritual power. For Clausewitz, the clock metaphor neglected the roles of ideas and uncertain factors in war, while the drama metaphor underestimated the role of reason. Clausewitz argued that war is a complex trinity of reason, emotions and decisions based on practice. Providing a new understanding of the complex relationship between war, Clausewitz's idea brings insights for contemporary war and the Enlightenment study.