Insufficient material and dead positions
When no series of legal moves can end in mate, the game is drawn at once.
The idea
When no legal moves can ever end in mate, the game is drawn.
- Black’s bishop stands on a light square.
- White’s bishop is on a light square too.
- The dark squares are never covered, so no mate can happen: a draw.
In a game: Before your time runs out, ask: could my opponent mate me by any series of moves?
How the lesson begins
A position is dead when neither player can checkmate the other by any series of legal moves, even if the other player helps. A dead position ends the game at once as a draw. Nobody has to claim it.
Here each side has a king and a bishop, and both bishops stand on light squares. A bishop never leaves its colour, so the dark squares are never covered and no king can ever be trapped. The game is drawn.
A question
Now the black bishop stands on a dark square. Is the game drawn at once?
Show the answer
No. A mate is still possible if one side plays badly, so the game goes on.
Right. With bishops on different colours, a king in the corner can be boxed in by its own bishop and mated. It almost never happens, but because it can, the position is not dead.