’Tis altogether impossible to give any definition of the passions of love and hatred; and that because they produce merely a simple impression, without any mixture or composition.
Love cannot be explained to someone who has never been in love.
Hume disserts in length on love and hatred, admitting beforehand that it will be impossible to define the passions. The only real knowledge that one may have is the experience of those passions.
Why read Hume’s Passions in that case?
If the essence of love or hatred cannot be coldly defined, it remains however possible to say something about those passions. Hume looks at observable effects, as one would before “laws of nature.”
The philosopher seeks to show that the rationalists are wrong to speak about certain things, especially surrounding feelings.
When one is in awe before a beauty, supports sympathetic relationships with others, or suddenly becomes incline to meanness towards someone—in short, when one becomes the slave of the passions—Hume seeks to value a certain type of knowledge: that which we know and feel “with the heart,” a type of truth that reason absolutely cannot grasp.