Why should I learn diagonal opposition?
For much the same reasons as you learn simple (or classical) and long-distance opposition: they’re different facets of the same problem, namely how to wrestle space away from the opposing King and attain the key squares that will yield you control of the game (if you are on the offensive) or allow you to defend a hard position (if you are on the defensive).
When do I use diagonal opposition?
When straight opposition (horizontal or vertical) is not possible right away, diagonal opposition is a way of forcing your opponent into it so that you can outflank him and take the key squares.
Link to Practice Problems
Diagonal opposition problem #1
Step-by-Step Guide On Diagonal Opposition
White to move.
- Kb6
This move prevents Black from jumping into c7 while preparing to advance the pawn.
- …Kc8
Trying to stop the pawn’s advance.
- c7
After c7, the only square the Black king could retreat to is d7.
- Kd7
This move is forced.
- Kb7
The only winning move. After this move, the White pawn is now safe for promotion.
- …Ke7
Any other move would still let the pawn promote.
- c8=Q
Promoting the pawn into a rook would still win. But promoting it into a knight or bishop would just throw your effort down the drain as it results to a draw.