Shogi glossary
Bishop's diagonal
Japanese: 角道
In shogi, the bishop's diagonal (kakumichi) is the line the bishop controls from its starting square; for Black's bishop on 8h the key one runs through 7g, 6f, 5e, 4d, 3c and 2b, and whether it is open shapes the opening.
The diagonal the bishop controls; opened or closed by the 7th-file pawn (3rd for White).
Opening and closing it
At the start the pawn on 7g blocks the line. Pushing it to 7f opens the diagonal; White does the same by moving the pawn from 3c to 3d. Once both are open, the bishops face each other and either side can exchange them. A pawn pushed to 6f (4d for White) closes the line again, which is what Yagura and most Ranging Rook setups do.
The silver on 7i
While both diagonals are open, the bishop on 8h relies on the silver on 7i for protection. If that silver steps up too early, the opponent's bishop captures on 8h and promotes to a horse. The same trap appears in many openings, so check the diagonal before moving the left silver.
Open or closed?
An open diagonal gives the bishop scope and keeps an exchange possible, which suits active openings such as Bishop Exchange, Side Pawn Capture and Gokigen Central Rook. A closed diagonal makes the opening calmer and lets both players castle without an early bishop trade.
FAQ
Why do Ranging Rook players push the pawn to 6f?
It closes the bishop's diagonal, so White cannot force a bishop exchange while Black swings the rook and castles. In the Fourth-file Rook it also gives the rook on 6h a pawn to back up.
Related
Terms:
Lessons: Static Rook vs Ranging Rook · The Yagura Castle · The Fourth-file Rook
Openings: Yagura · Bishop Exchange · Gokigen Central Rook
I don't do defense. Hope you brought a castle!
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