This also comes from David Hume, "Of the Association of Ideas," section 3 in An Enquiry Concerning Human Understanding, ed. Eric Steinberg, 2nd ed. (1748; repr. Indianapolis, IN: Hackett Classics, 1993); and Hume, A Treatise of Human Nature, Book 2: Of the Passions, parts 1 and 2 (Mineola, NY: Dover Philosophical Classics, 2003).