The Value of Castling

Look at the position in the following diagram. Can you tell what the previous moves were? Before you leave in a huff, muttering, 'Another stupid question from a stupid blog', consider the following three variations:-

• 1.e4 e5
• 1.e4 e5 2.Ke2 Nf6 3.Ke1 Ng8
• 1.e4 e5 2.Nf3 Ke7 3.Ng1 Ke8

Each of those variations leads to the diagrammed position, but the final positions are not at all equivalent. The first variation is a normal open game, the second is a line where White can't castle, and the third is a line where Black can't castle.

A few months ago, in a series titled Practical Evaluation, I wrote a post about less known material imbalances: One Imbalance Leads to Another. One of those imbalances was

• 1.0 - Value of castling

where '1.0' is the well-known value of a Pawn. Ever since encountering that statement by GM Kaufman, I've wondered if there was any way to verify it. I've also wondered about the value of castling O-O as opposed to O-O-O. Armed with the three variations at the beginning of this post, I can plug the resulting positions into an engine and record the results.

Of course, there's no reason to choose the position after 1.e4 e5. I could have also chosen 1.d4 d5, or 1.c4 c5. I could have also invented positions identical to 1.e4 e5, where one or both sides have forfeited the right to castle to one side or the other. Looks like I have a neat little tool for further exploration.

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Later: In fact, the moves 1.c4 c5 don't serve the same purpose, because they don't provide an outlet for the Kings. The moves 1.f4 f5, would do the trick, although the esthetics aren't the same.