Definition
A shared fiction is a belief — about a god, a nation, a corporation, a debt, a law, a brand — that is held by many Sapiens at once, that coordinates their behavior, and that has no existence in the physical world outside the minds of the believers. The dollar is a shared fiction. So is Google. So is Argentina. So is the rule of law. None of them can be picked up; all of them shape how the people who believe in them act.
Harari treats shared fiction as the cognitive primitive of Sapiens success. Most animals — including other great apes — cooperate only with individuals they personally know and trust. Sapiens cooperate with millions of strangers because they all hold the same fictions in mind at the same time. A shared fiction does not need to be true to work; it only needs to be widely enough believed that everyone behaves as if it is.
Why it matters
How it works
A shared fiction works because it is collectively believed, embedded in institutions, and enforced by social behavior. A dollar bill is paper, but everyone treats it as worth what it claims to be, banks honor it, courts enforce contracts denominated in it, and tax authorities demand it back at year-end. Each of these reinforces the others; no individual can opt out alone.
Crucially, the fiction is inter-subjective rather than subjective or objective. It does not depend on any one mind, and it does not require a physical truth-maker. It lives in the network of all the minds that hold it. As long as the network sustains it, it operates with the force of any physical fact. This is why questioning a shared fiction philosophically does not dissolve it operationally — Harari may know money is a fiction, but he still has to pay his rent.