from leading to injury, and animate a pack of hunting dogs beyond their individual level of excitement. In general, Hume remarks, the psychological mechanisms at work do not require any sophisticated "force of reflection or penetration": "[e]very thing is conducted by springs and principles, which are not peculiar to man, or any one species of animals". Part 3: Of the will and direct passions Sections 1–2 In Part 3, Hume begins examining the motives that bring us to action. After a glancing mention of the direct passions and a perfunctory definition of the will as a mere impression we feel, he confronts the hoary philosophical problem of free will and determinism, dedicating two sections to a defense of soft determinist compatibilism. In the first section, he makes a case for "the doctrine of necessity". The issue, as Hume sees it, is whether human action is determined by a necessity comparable to "physical necessity"—the necessity that governs physical objects. But since, according to Book 1, physical necessity is nothing more than constant conjunction and the causal inferences drawn by the human mind, the issue then comes down to this: is there a regular correspondence between human action and human psychology, and do we base causal inferences upon such regularities? Hume thinks the answer to both questions is obviously in the affirmative: the uniformity found in the world of human affairs is comparable to that found in the natural world, and the inferences we base on "moral evidence" (concerning human psychology and action) are comparable to the inferences we base on natural evidence (concerning physical objects). Thus, given Hume's idiosyncratic account of necessity, it is hard to deny that human action is governed by necessity. In the next section, Hume challenges "the doctrine of liberty"—the view that human beings are endowed with a distinctive kind of indeterministic free will—by setting out and debunking "the reasons for [its] prevalence". First, since we confuse necessity with violent constraint, we end up confusing freedom from necessity (the indeterministic "liberty of indifference") with freedom from violent constraint (the compatibilist "liberty of spontaneity"). As a compatibilist, Hume accepts the latter kind of free will, deeming it "that species of liberty, which it concerns us to preserve" and even "the most common sense of the word"; but he rejects freedom from necessity as either "absurd" (being nothing more than sheer "chance") or else "unintelligible". Second, we are deceived