pain is within our power to obtain. Second, there are those direct passions which "arise from a natural impulse or instinct, which is perfectly unaccountable": here Hume mentions benevolence, anger, hunger, and lust (in section 3 he had mentioned self-preservation and the love of one's children). These diverse instinct-based passions, Hume writes, "produce good and evil [i.e., pleasure and pain]", as opposed to the other direct passions, which arise from pleasure and pain. Hume spends the rest of the section on hope and fear, starting with a simple account based on probability. In conditions of uncertainty, as the imagination fluctuates between a pleasant scenario and an unpleasant scenario, the passions follow suit, fluctuating between joy and grief. And since different passions can blend together (like the lingering notes of a string instrument), the mixture of joy and grief will end up producing either hope or fear. But "contrary passions" interact differently depending on what they are directed at: the passions have no influence on each other if their objects are completely unrelated (e.g., joy at x, grief at y); the passions tend to cancel each other out if they have the same object (e.g., joy at x, but also grief at x); and the passions tend to blend together if they have "contradictory views of the same object" (e.g., joy at x, grief at not-x). Next, Hume tries to confirm and extend his account, noting that hope and fear can arise from "all kinds of uncertainty": thus fear can be produced by the mere thought of a possible evil if it is great enough, the immediate presence of a potential evil known to be impossible, the certainty of an evil too horrible to think about or whose precise nature is unknown, or anything extremely surprising. Even utterly irrelevant circumstances, or something expected to be pleasant, can call up fear if shrouded in uncertainty. Hume closes the section by begging off any discussion of subtle "variations" of hope and fear, or of the role of the will and the direct passions in animals. Book 2 finishes with a brief section on curiosity—"the love of truth", which leads us to take pleasure in intellectual pursuits and achievements. For both the abstract truths of "mathematics and algebra" and the real-world truths of "morals, politics, natural philosophy", we do not care much about truth "merely as such". Instead, there are three other factors chiefly