>[!abstract] >In game theory and economics, **complete information** means that all players know the game’s full structure (players, strategies, payoffs, and types) while **perfect information** means that at every decision point, each player knows the current state and all the past moves. These two dimensions are [[Orthogonality|orthogonal]] so it is possible to identify four cases: complete and perfect, incomplete and perfect, complete and imperfect, incomplete and imperfect. >[!example] >- **Complete and perfect:** Chess players have both complete (they know all the rules and payoffs) and perfect information (they observe others' past moves up to the decision point). >- **Complete and imperfect:** Rock-paper-scissors players have complete (they know all the rules and payoffs) but imperfect information (moves are made simultaneously so they remain unobserved at the decision point). >- **Incomplete and perfect:** English auction participants who take turns announcing their bids have incomplete (they do not know others' payoffs, i.e., true valuations of the object) but perfect information (they know all prior bids at the decision point). >- **Incomplete and imperfect:** Poker players have incomplete (others' payoffs are hidden because they depend on their cards) and imperfect information (they never know the full game's state at the decision point). >[!related] >- **North** (upstream): — >- **West** (similar): — >- **East** (different): — >- **South** (downstream): —