The following five sections examine the factors which give passions their motivational force. Unsurprisingly, the violence of a passion makes it stronger; but even a calm passion can be extremely strong due to "repeated custom and its own force", especially when it has been "corroborated by reflection, and seconded by resolution". Nevertheless, since "[g]enerally speaking, the violent passions have a more powerful influence on the will", Hume focuses on the factors which increase the violence of passions. First, when a "predominant passion" is accompanied by other "inferior" passions, it can acquire violence by "swallow[ing them] up": e.g., strong love can be made more violently passionate by a touch of anger. Other psychological phenomena (e.g., opposition, uncertainty, obscurity) can produce the same effect by stimulating us with agitation and mental effort. Next, "custom and repetition" can both leave us with a direct inclination to perform the activity we are repeating and also affect the violence of related passions. Hume discusses three stages of repeated activity: (1) The sheer novelty of unfamiliar activities makes our feelings more intense, either magnifying our pain or adding on the pleasure of "wonder [and] surprise". (2) An activity performed with "moderate facility" is "an infallible source of pleasure" (cf. "flow"), sometimes even converting pain into enjoyment. (3) But excessive repetition can make formerly pleasant activities so dull as to be unpleasant.
