A central idea of Foundation is that science may someday be able to predict the future well enough to guide societies through crises. For Hari Seldon, the purpose of such predictions is to save human civilization, and his new science of psychohistory attempts to do just that. Two major problems stand in the way of such a project: how to accurately predict the actions of huge populations, and how to account for individual agents who may later jeopardize the accuracy of those predictions by altering the course of history. These problems are defined by the sociological theory of the uncertainty principle, which posits that a self-aware population becomes unpredictable because awareness of a potential future allows individuals to alter their course of action, rendering initial predictions inaccurate. Seldon resolves the threat of the uncertainty principle to his centuries-long plan with a single, ongoing solution: limiting the possible actions of future actors.

Hari Seldon’s science of psychohistory solves the first, more technical problem of how to predict the future accurately. He addresses this puzzle by ignoring the influence of individuals, who are highly unpredictable, and focusing on masses of humans, whose future behavior can be calculated much more precisely.