Cheaper oil is good for the economy — it’s basically the equivalent of a tax cut. Unless it’s bad for the economy, which can be the case if falling prices spur deflation and hurt countries and companies that depend on oil exports. Whether the impact is good, bad, or a little of both, will depend on how long prices stay low. If cheap oil is the result of a drop in demand (from an ailing Chinese economy, for example), prices will rise when the economy picks up. If lower prices stem from increased supply (from the shale boom, say), then cheap oil is here for at least a while. Two things are certain: There’s still a finite amount of oil in the world, and the economy needs oil to function. That suggests oil prices will increase someday, although no one is sure whether that will happen as soon as the spring or as far off as the 2050s. Unless something really is different this time. Those are dangerous words, and it’s always safer to assume that history does, in fact, repeat itself. There is a chance, though, that the drop in oil prices could inspire a change in energy policy, in which case there may be lasting consequences.