Diagonal opposition

In its basic form, diagonal opposition occurs when the kings stand on the same diagonal with one empty square between them. The kings do not block each other head-on along a horizontal row or vertical column, but their spacing and the move order determine the direction in which the position can be converted.

The player who is not to move normally has diagonal opposition in an open position. If the opposing king advances one way, that player can answer so that the kings reach direct opposition on the horizontal row or vertical column that serves the intended goal. Diagonal opposition therefore often acts as a bridge between two routes.

Direction matters

Not every conversion is equivalent. When attacking, the king must turn the relationship toward the area it wants to enter or toward a key square. When defending, it must convert toward the route that blocks the opposing king. Preserving the geometry in the wrong direction may surrender the very square that mattered.

Distant opposition may also pass through a diagonal relationship before the kings meet at close range. As with every form of opposition, pawns and board edges can change the result. So can a waiting move, which preserves one task while making the opponent move first at the decisive moment. The reply must therefore be checked in the actual position.