"Willpower" and "volition" are colloquial and scientific terms (respectively) for the same process. When a person "makes up their mind" to do a thing, that state is termed 'immanent volition'. When we put forth any particular act of choice, that act is called an emanant, executive, or imperative volition. When an immanent or settled state of choice controls or governs a series of actions, that state is termed predominant volition. Subordinate volitions are particular acts of choice which carry into effect the object sought for by the governing or "predominant volition".