The diagonal opening

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Why it is called diagonal

Black's first move builds a row of three black discs across rank 5: d5, e5 and f5. White then has exactly three legal answers, and each one produces its own straight line of three white discs. Here White plays f6, which flips e5 and leaves white discs on d4, e5 and f6.

That white line runs on a diagonal, so the opening is the diagonal one. The other two answers give lines that run at right angles to Black's row or alongside it, which is where perpendicular and parallel get their names.

The move that matters: 2... e6

Black has four legal replies, but only three of them lead anywhere the catalogue has bothered to name, and one of them carries almost the whole family. That move is e6.

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This position is symmetric about the long diagonal from a1 to h8. Fold the board along that line and every disc lands on a disc of its own colour. White's two remaining moves, d6 and f4, sit opposite each other across the fold, so whichever one White chooses the resulting position is the same shape reflected.

That is why nearly every diagonal opening in the catalogue appears twice. There are 31 named diagonal openings, written down as 59 move sequences. Both sequences are real transcripts you might play, and both deserve the same name.

The Cow and what grows out of it

The best known diagonal opening is the Cow, 1. f5 f6 e6 d6 c5. It is worth learning first because so many other named lines run through it.

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Move five is Black's big fork. Five other squares in that same position carry names of their own, which is a useful way to see how much one disc changes the shape of a game.

• c3 is the Buffalo, also called the Kenichi Variation.
• d7 is the Raccoon Dog.
• e7 is the Heath, also called Tobidashi, "jumping out".
• f7 is the Snake, also called the Peasant.
• g7 is the X-square Opening.

Carry on down the Cow and White almost always plays e3. Black then picks between two well-studied moves. d3 gives the Rose-v-Toth. e7 gives the Cow Bat, which older books call the Bat or the Cambridge.

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What the diagonal feels like to play

Compared with the perpendicular, diagonal games tend to reach edge fights sooner. Discs get fed onto the top and left edges early, and an edge that is one disc short of being safe is the classic way to lose a corner. If you play the diagonal, spend your study time on edges and corners rather than on move lists.

None of that means the diagonal is risky. Both it and the perpendicular are played at the top level and neither is known to be losing. The parallel is the one White is warned off.

Keep reading

• All Othello openings, the full index and how the families work.
• Perpendicular openings, White answers f5 with d6.
• Parallel openings, White answers f5 with f4.
• Opening strategy, the ideas underneath the names.
• Play a diagonal opening, paste any sequence above into the board.