The Case for Strong Longtermism
H. R. G. Greaves, William MacAskill
Abstract
Abstract This essay sets out the case for strong longtermism: the thesis that impact on the far future is the most important feature of our actions today. We discuss both axiological and deontic versions of this thesis. We argue that there exist at least some actions available to society—specifically, actions aimed at reducing existential risks—that deliver significantly larger expected benefits in the far future than any available action delivers in the nearer future. We then argue from this claim to axiological strong longtermism. The argument is robust to plausible deviations from expected utility theory, to variations among a wide range of the more plausible views in population ethics, and to differing views on the question of whether the continuation of human civilisation would on balance be a good or a bad thing. We also suggest that, given the size of the stakes involved, this axiological thesis supports a corresponding deontic thesis.