Sunday, February 1, 2009

Canterbury Tale

Rowan Williams, the Archbishop of Canterbury

On Blue Devil Knight's resurrected blog, he posted Part 6 of his review of Rowson's Chess For Zebras. Because of BDK's discussion, I bought Chess For Zebras, mostly from the good things I was reading, but partly because I own Chess For Tigers by the late Simon Webb and I can't resist collecting a set of books on an animal theme. I also own The Hippopotamus Rises, but it's not quite in the "Chess for (animal name here)" format. The discussion turned to Rowson's opinion of how we think about a chess position and that Rowson doubted the utility of the natural language narrative. His point was that NARRATIVES correlate more with weaker amateurs while IMAGES about how the position is resolved and evaluated correlate better with how strong professional players process the position. Not that I wish to contradict Rowson or even BDK, but I found it useful to understand the following endgame position in terms of language. Otherwise it didn't make sense to me. Plus, my memory requires all kinds of verbal and nonverbal underpinnings these days.

Centurini 1856. White to play and win.

This position was first shown to me by a friend at the club. He whispered a couple sentences to a low-rated kid to defend the position. I floundered about for a while gaining nothing except that I noticed that the kid kept returning to attack the d6 square. Only by inference did I begin to suspect there was something crucial about d6. My friend showed me the solution, but it didn't sink in why the d6 square was so important until four years later (a month ago) when I could verbalize what was going on.

We begin with White's winning plan, Plan A: to evict the Black bishop from the h2-b8 diagonal by placing his own bishop on that diagonal. Since c7 is guarded twice and the Black bishop can mark time on the diagonal, then the route to victory has to go partly through...

Plan B: to maneuver the bishop through the g1-a7 diagonal to a7 and then to b8. Will Plan B work? The only way for Black to hang on once the White bishop gets to b8 is to move his own bishop to the g1-a7 diagonal, wait for the enemy bishop to move out on the diagonal h2-c7 diagonal so that the pawn can advance, and then post his own bishop on a7 to kill the newly born Queen. But, assuming White retreated his bishop to e5, f4, g3, or h2 can then put his own bishop en prise on the g1-a7 diagonal to distract the Black bishop at a7. The pawn can then queen by force.

So Plan B works if Black simply allows it. In a sense, this endgame helps support the endgame Theory of Two Weaknesses. If there are two weaknesses to spread the defense enough, the stronger side can win by quickly switching targets. But Black has a defensive resource in that his king at c6 can move to a6 whenever the White bishop gets close to the g1-a7 diagonal.

Centurini 1856. White to play and win.

From the diagram position, 1.Bh4 Kb6 2.Bf2+ (2.Bd8+ Kc6 simply repeats the position.) Ka6 and the a7 square is defended. If the White bishop tries to tack back to d8, the Black king comes back to c6 to prevent Bc7: e.g. 3.Bd4? Bd6 4.Bf6 Kb6 5.Bd8+ Kc6 and now the position only differs in that the Black bishop is at d6 instead of h2.

This opens a new possibility that is not quite enough. 6.Be7 tries to distract the bishop from its guardianship of the b8 square, but 6...Bh2 Black wants none of it and returns to a square where it cannot be chased.

Now notice that the White bishop at e7 could get to a7 in two moves if only the Black king at c6 wasn't covering the pivot square on c5. This provides the winning idea and is the key to understanding why d6 is so crucial to this endgame. So White can take another crack at it. 7.Bh4 Kb6 8.Bf2+ Ka6 9.Bc5! preventing Bd6.

9...Be5 10.Be7 Kb6 11.Bd8+ Kc6 12.Bf6 Bh2

Notice that this diagram after move 12 is different from the diagram after move 6 in that the bishop can now pivot through d4 to get to a7 instead of c5. The Black king is now caught with his pants down. 13.Bd4! Kb5 14.Ba7 Ka6 15.Bb8 Bg1 16.Bg3 Ba7 17.Bf2 and the pilgrims finally get to Canterbury.

My tale of this endgame is that White must maneuver his bishop through d6 on his way to e7 and d8 in order to prevent the Black bishop from being in the optimum square at d6. When the White bishop pops back out from d8, it can quickly pivot over to a7 without running into the Black king. Whether this information is "better" stored in my brain as an image or as a narrative surrounding the d6 square, I'm not sure. But now that I can say it aloud, I feel that I understand it or grasp it, which is better than feeling like it is a memory that will run away as soon as my hippocampus turns its back.

1 comment:

Eric Shoemaker said...

Hi Ernie, my favorite tale is Chaucer's "Wife of Bath's Tale" in the Canterbury Tales. But that is pretty normal among English Literature Majors.