Besides we may consider, that when we receive harm from any person, we are apt to imagine him criminal, and ’tis with extreme difficulty we allow of his justice and innocence. This is a clear proof, that, independent of the opinion of iniquity, any harm or uneasiness has a natural tendency to excite our hatred, and that afterwards we seek for reasons upon which we may justify and establish the passion. Here the idea of injury produces not the passion, but arises from it.
Fine observation on the part of Hume: hatred does not come from opinion, but vice versa. Worse: a person affected by such passion yet summons reasons to justify it, even accuse another who could be held responsible for the harm they have received.
The passions, more or less exaggerated, tend to invoke rational explanations. To be oneself the cause of one’s own humility intensifies the painful aspect of the sensation (I have only myself to blame for my failure in school, my clumsiness in society, my misfortune in relationships); but if the cause is external (a natural disaster, an economic crisis, or simply another person), the force of the passion is diminished, since it can be blamed on something else, someone else.
It is once again an argument in favour of the primacy of the passions: an unpleasant passion makes one justify it, after the fact (which is not surprising, given that Hume has stated his position on the irrational character of human beings).
Reason is a slave to the passions.