Hume begins his discussion of ‘liberty and necessity’ with some philosophical methodology that it is wise to keep in mind—namely, that in philosophical discussions it is of the first importance to get clear on what the terms under discussion mean, if we are to avoid ‘obscure sophistry’ or ‘beat[ing] the air in. . . fruitless contests’ (¶1–2).1 Hume’s hope in this particular instance is that with intelligible definitions, the controversy over the compatibility of free will and determinism will dissipate. Hume, however, straightaway disobeys his own advice, for nowhere does he give a clear definition of ‘necessity’. However, we can easily enough reconstruct one from his remarks at ¶¶4–5: