 It is natural to distinguish between causes and background, or enabling, conditions. For instance, suppose that you strike a match and it lights. It’s natural to cite your striking the match as a cause of its lighting, but it’s far less natural to cite the presence of oxygen as a cause of its lighting, even though, without the oxygen, the match wouldn’t have lit. There’s some inclination to say that the presence of oxygen merely enabled the strike to cause the match to light, but did not cause it to light itself. Lewis (1973) echoes a traditional, dismissive, attitude when he refers to the distinction between causes and background conditions as “invidious discrimination” (see also Mill 1843 and J. L. Mackie 1974). On this view, the distinction is pragmatic, unsystematic, and dependent upon our interests. Alien scientists from Venus—where there is no oxygen in the atmosphere—might find it incredibly natural to point to the presence of oxygen as a cause of the fire. On the traditional view, neither we nor the Venusian scientists are making any objective error; we each simply have different expectations about the world, and so we find some features of it more noteworthy than others. There are ever-so-many causes out there, but we select some of them to call causes. The others, the ones we do not select, are regarded as mere background conditions.