What is parity in Reversi?
Parity is the endgame idea that turns close Reversi games. It sounds abstract, but it comes down to counting empty squares. Here is how it works.
The last move usually flips the most
Late in a game the board breaks into small empty regions. Whoever plays the last disc into a region typically captures a big line, because their opponent has no reply. So the goal is to arrange the move order - the parity - so that you, not your opponent, place that final disc in the biggest pockets. Counting the empty squares in each region tells you who moves last.
Combining parity with the rest
Parity works alongside corner control and mobility: you keep your options open through the middlegame, then use parity to cash in during the last dozen moves. It is a subtle skill, and one of the clearest signs of a strong player. Try counting it out in a slow game on the Othello board.
Related questions
How do you win at Reversi?
Winning Reversi comes down to three ideas: grab the corners safely because corner discs can never be flipped; play for mobility by keeping many good moves for yourself and few for your opponent; and control parity so you make the last move in each region. Chasing raw disc count early is usually a mistake.
What is mobility in Reversi?
Mobility is the number of good legal moves available to you. Strong Reversi play keeps your own mobility high while squeezing your opponent's down, so that eventually they are forced into bad moves - like giving up a corner. Mobility usually matters far more than how many discs you currently own.
Why are corners so important in Reversi?
Corners are the most valuable squares in Reversi because a disc placed in a corner can never be flanked or flipped. It becomes a permanent anchor that lets you flip long lines for the rest of the game and stabilise entire edges. Most Reversi games are decided by who wins the corners.