This book is about longtermism: the idea that positively influencing the longterm future is a key moral priority of our time. Longtermism is about taking seriously just how big the future could be and how high the stakes are in shaping it. If humanity survives to even a fraction of its potential life span, then, strange as it may seem, we are the ancients: we live at the very beginning of history, in the most distant past. What we do now will affect untold numbers of future people. We need to act wisely.

I now believe the world’s long-run fate depends in part on the choices we make in our lifetimes. The future could be wonderful: we could create a flourishing and long-lasting society, where everyone’s lives are better than the very best lives today. Or the future could be terrible, falling to authoritarians who use surveillance and AI to lock in their ideology for all time, or even to AI systems that seek to gain power rather than promote a thriving society. Or there could be no future at all: we could kill ourselves off with biological weapons or wage an all-out nuclear war that causes civilisation to collapse and never recover.

For these reasons changing values has particularly great significance from a longterm perspective. Looking to the past, we see that such changes have had an enormous impact on the lives of billions of people. Looking to the future, if we can improve the values that guide the behaviour of generations to come, we can be pretty confident that they will take better actions, even if they’re living in a world very different from our own, the nature of which we cannot predict.

This suggests that, as longtermists, when trying to improve society’s values, we should focus on promoting more abstract or general moral principles or, when promoting particular moral actions, tie them into a more general worldview. This helps ensure that these moral changes stay relevant and robustly positive into the future.

Positive moral change is not inevitable. It’s the result of long, hard work by generations of thinkers and activists. And if there’s any change that’s not inevitable, it’s concern for future people—people who, by virtue of their location in time, are utterly disenfranchised in the world today.

If we are careful and far-sighted, we have the power to help build a better future for our great-grandchildren, and their great-grandchildren— down through hundreds of generations. But we cannot take such a future for granted. There’s no inevitable arc of progress. No deus ex machina will prevent civilisation from stumbling into dystopia or oblivion. It’s on us. And we are not destined to succeed.