noun
voluntarist
A person who adheres to voluntarism, the philosophical doctrine that the will is the fundamental principle of reality or that emphasizes the primacy of the will over reason.
彼は主意主義者として、理性よりも意志の力を重視する。
As a voluntarist, he emphasizes the power of the will over reason.
主意主義 is the doctrine of voluntarism, while 主意主義者 refers to a person who subscribes to that doctrine.
Compound of 主意 (shui, 'primacy of the will') + 主義 (shugi, '-ism') + 者 (sha, 'person'). The term is a direct translation of the Western philosophical concept of voluntarism.