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A portrait illustration of Hilary Greaves. Rebecca Clarke for Vox

Hilary Greaves is the world’s leading philosopher of the long-term future

The Oxford researcher is asking hard questions about what we know, how soon we can know it, and why it matters.

So, you want to make the world a better place. You want your net effect on other people’s lives to be positive, for them to be better off because of your actions. This is a noble impulse but one fraught with knotty questions. One of the thorniest: How do you actually know what the consequences of your actions are with any kind of certainty? In particular, how can you understand the consequences of your actions many, many decades into the future? Suppose you’re a firefighter in the 1890s working in the Austrian city of Linz, and you extinguish a flame threatening to consume a whole apartment building. This seems good, until decades later when you realized you prevented Adolf Hitler from dying in childhood. You saved some lives but in doing so failed to save millions more.

In philosophy this is known as the problem of “cluelessness.” It’s a particularly big problem for consequentialists, philosophers who believe that morality is entirely about taking actions or following rules that result in good consequences. But no ethicist is indifferent to consequences, and all else being equal almost all would agree that doing more rather than less good in life is desirable. Consequences matter a lot to basically everyone, and if we’re clueless about the consequences of our actions, we’re in deep trouble.

Leading the way out of that kind of trouble is Oxford philosopher Hilary Greaves. Initially specializing in the philosophy of physics and the interpretation of quantum mechanics, she made a hard pivot mid-career to focus on ethics and soon established herself as a leading theorist working on the problem of cluelessness. She’s also become a leading researcher on moral uncertainty, how to act in situations where the correct moral outlook is unclear — another, no less vexing, form of human ignorance that can imperil attempts to make the world a better place.

Greaves has also come to the somewhat counterintuitive conclusion that the problem of cluelessness strengthens the case for longtermism by focusing strongly on the far future. Whereas near-term interventions, like helping farm animals or distributing anti-malarial bed nets, will doubtlessly have long-term consequences that are nearly impossible to predict, interventions to prevent, say, human extinction seem more reliably positive in their consequences. One of the most precise statements of the longtermist view, a paper aptly titled “The Case for Strong Longtermism,” comes from Greaves and Will MacAskill.

While she may not have her coauthor’s outsized public profile, Greaves is responsible for a lot of the academic philosophical work that underpins longtermist thought, which is now driving billions in charitable investments. That alone positions her as one of her generation’s more influential philosophers — hopefully for the better, but she’d be the first to say we need to wait a good deal longer to be sure.