William MacAskill

Scottish philosopher at the University of Oxford and one of the principal architects of the effective altruism (EA) movement — the view that we should use evidence and reasoning to do the most good we can with our resources, including our careers and charitable giving.

MacAskill co-founded two EA flagship organisations: 80,000 Hours, which advises people on high-impact careers, and Giving What We Can, which hosts pledges to donate a fixed share of income to effective charities. His books Doing Good Better (2015) and What We Owe the Future (2022) are the movement’s most widely read popular texts. What We Owe the Future makes the case for longtermism — the view that improving the long-run trajectory of civilisation is the most pressing moral priority — and was received as one of the most significant works of applied ethics of its decade.

Core positions

MacAskill’s signature move is moral uncertainty managed as a portfolio: rather than committing to utilitarianism or any single moral theory, he holds calibrated credence across multiple frameworks and acts on their weighted average. This meta-level approach lets him take scale-sensitive reasoning seriously — more lives saved is better than fewer — without committing to every implication of strict expected-value maximisation (he explicitly declines, for instance, to take a 51/49 double-or-nothing gamble on civilisation).

On longtermism, his core argument is structural: at any plausible rate of sustained growth, the number of people yet to live vastly outnumbers those alive today. Reducing existential risk — extinction or permanent collapse — is therefore exceptionally high-leverage, because it preserves access to all that future value. He argues we live in an unusually ‘hinge-y’ moment: a narrow window of anomalously rapid technological change that cannot compound indefinitely without consuming resources that do not exist.

MacAskill has also shifted over time toward taking culture seriously as a causal variable. He credits Joseph Henrich’s work on cultural evolution with changing his view of human motivation from homo economicus (self-interest) to homo culturalis (people acting on shared visions of how the world should be). He now describes EA itself as a form of cultural innovation — an attempt to propagate a subculture of impartiality, epistemic rigour, and altruistic concern, analogous to the cultural shift that produced the scientific revolution.

In the wiki

• William MacAskill on Effective Altruism, Moral Progress, and Cultural Innovation — Conversations with Tyler, Ep. 156: moral uncertainty, longtermism, expected-value theory, and EA as cultural innovation