Same position

Two moments in a game count as the same position only when more than the board picture matches. The same player must have the move, pieces of the same kind and color must occupy the same squares, and all possible moves for both sides must be the same.

Complete identity despite different histories

Two routes to the same state

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Nb1

Ng8

Nc3

Nf6

Nb1

Ng8

The knights start on a3 and h6.

A different starting point

The knights are on a3 and h6. This is not yet the state that will be compared.

1. The knights start on a3 and h6.

The side to move is essential. An identical arrangement with White to move and Black to move represents two different positions because the available actions and the immediate meaning of checks and threats differ.

Same placement with a different side to move

The board matches, the turn does not

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Kb1

Kg8

Kb2

Kh8

Ka1

Reference with White to move

The pieces occupy the reference squares and White has the move.

Rights that are not obvious from the pieces also matter. If an en passant capture, the special pawn capture available immediately after an opposing pawn advances two squares, was previously possible but is no longer possible, the positions are not the same. They also differ if a king or rook moved and lost castling rights, the right to make the special king-and-rook move, even after returning to the original squares.

Same placement with different castling rightsSame placement with a different legal en passant capture

A right that does not return

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Rh2

Na6

Rh1

Nb8

The king and rook retain kingside castling rights.

Right retained, move blocked

Both sides retain kingside castling rights. The knight on g1 prevents White from castling immediately.

1. The king and rook retain kingside castling rights.
2. The knight on g1 blocks immediate execution.

This definition governs repetition. A third occurrence may lead to a draw after a correct claim, a formal request to the arbiter, by the player having the move; a fifth occurrence makes the game drawn automatically. The written move number and the players' remaining clock times are not part of this rules-based comparison.