What Is Triangulation in Chess?

How triangulation works

Many king and pawn endings come down to a key position that the attacker wins only if the defender has to move. If it is the attacker's turn instead, the attacker needs to pass, which is not allowed. Triangulation is the way to pass with the king.

The attacking king walks around a small triangle of three squares and arrives back where it started after three moves. If the defending king has only two squares it can use while still guarding everything, it cannot copy the triangle. After its two moves it is back where it started too, but now it is the defender's turn.

When it works

Triangulation needs two things. The attacking king must have room to make the triangle without giving up anything important, and the defending king must be short of space, usually because of the edge of the board, its own pawns, or squares it must keep guarding.

If the defending king can also triangulate, it simply mirrors the maneuver and nothing changes. That is why the trick works best when the defender is pushed to the side or back of the board.

How to find it

First find the key position: the one you win if the opponent is to move. Then check whether you can reach it with the opponent to move from where you are now. If the kings are already in that position with you to move, look for a set of three squares near your king, each of which keeps the defender tied down. Walking around them hands the move to the opponent.

Common questions