Direct opposition

Direct opposition occurs when the kings stand on the same horizontal row, called a rank, or vertical column, called a file, with exactly one empty square between them. Because each king controls that middle square, neither king can advance toward the other.

In a simple position, the player who is not to move has direct opposition. The king that must move has to retreat or step aside. The other king can then advance toward an important square or follow to preserve the barrier. This obligation turns king geometry into a basic form of zugzwang, a situation in which being required to move makes the position worse.

Attack and defense

The pawn side may use direct opposition to drive the defending king away and reach a key square. The defender may use the same relationship to deny entry and preserve a draw. The king placement therefore has no fixed value by itself; its meaning depends on whose turn it is and which square each side needs.

An available pawn move can change the effective move order. Instead of moving the king, a player may spend that pawn move and return the obligation to the opponent. A player may also use distant opposition or diagonal opposition to approach the direct form by a different route.