Check, Checkmate and Stalemate: the difference that decides the game

Check means your king is under attack and you must deal with it on the next move. Checkmate is that attack with no legal answer left: the game ends on the spot. Stalemate is the dangerous opposite, the player to move is not in check and still has no legal move at all, and the game is a draw. Mixing up those last two throws away won games.

Check: the king is under attack

A king is in check when an enemy piece attacks the square it stands on and could capture it next move. Check is not a special move and you do not have to announce it out loud: it is a state of the board. In notation, + marks check and # marks mate. The piece letters are K for king, Q for queen, R for rook, B for bishop, N for knight.

One rule holds everything else together: you may never leave your own king in check. You cannot move a piece pinned in front of your king, and you cannot castle out of check, across an attacked square, or onto one. The king is never actually captured: when no answer is left, the game ends before that happens.

1. Move the king. Kd1, Kd2, Kf1 and Kf2 all leave the e-file. Ke2 solves nothing: the king stays on the same file, still attacked, so that move is illegal.
2. Block the line. Be2 puts the bishop in front of the king. Blocking only works against a rook, a bishop or a queen, the pieces that attack from a distance.
3. Capture the checking piece. Nxe8 takes the rook off the board and the attack stops existing.

Two exceptions are worth memorizing. Against a knight check or a pawn check there is no blocking: the knight jumps over everything and the pawn attacks from next door, so you are left with capture or run. And against a double check, where two pieces attack the king at once, the only answer is a king move: no capture deals with two attackers.

Checkmate: check with no answer

Checkmate is a check where none of the three answers exists. No safe square, nothing to block with, nothing that can capture the attacker. The game ends at once, with no king capture and no counting of material: whoever gives mate wins, even ten pieces down.

Every mate combines two things: attacking the king's square and taking away the squares around it. Sometimes the attacker removes those squares, sometimes the defender's own pieces do. The fastest possible mate in chess shows both ideas already on move two:

Look at what f3 and g4 did: they developed nothing and emptied the squares around the king. Almost every quick mate has that signature: active pieces on one side, empty squares around the king on the other.

The back-rank mate

One of the most common mates in real games is the back-rank mate. The king castled, settled in behind its three pawns and never left. A rook or a queen lands on the last rank, and the pawns that were protecting the king become the walls of the cell.

Run the three answers. Escape: f8 and h8 sit on the rook's rank, f7, g7 and h7 hold Black's own pawns. Block: no black piece reaches e8 or f8. Capture: nothing attacks d8.

Stalemate: no check and no move

Stalemate happens when the player to move is not in check and still has no legal move. Every square around the king is covered, and the remaining pieces, if any, are frozen. The result is a draw, half a point each, no matter who was ahead on material.

This is the classic trap. King and queen against a lone king is the first mate anyone learns, and the winning side still picked the wrong square. One move earlier, with the queen on g5, Qg7# was mate: the queen steps next to the black king, defended by the king on f6, so nothing can take her. By going to g6 instead, she removed all three king squares without giving check, and a full point became half a point.

Preventing it takes two seconds. When you are far ahead, ask before releasing the piece: after this move, does my opponent have any legal move at all? If the answer is no and the move is not a check, play something else. Leaving the enemy king one free square costs nothing when you are a queen up.

The practical lesson, from both sides

• When you are winning big: give the enemy king air, and distrust any move that leaves your opponent with nothing to touch.
• When you are losing badly: hunt for stalemate. Give away the pieces that can still move and steer toward positions where every remaining move would be illegal.
• Always: after each opponent move, look for checks against you first. Seeing the check early prevents most careless losses.
• With heavy pieces on the board: count the defenders of your back rank before every trade. Back-rank mates start with a trade played on autopilot.

Stalemate is only one way a game can be drawn: threefold repetition, the 50-move rule and insufficient material also split the point.