|How was this position arrived at?|
In most chess problems the goal is to mate in x moves or win material, but in retrograde problems you are asked to determine moves that lead up to the position. Of course, the moves have to legal, not necessarily good.
In retrograde problems, as well as in standard problems, castling is assumed to be legal unless it can be proved otherwise. An en passant capture, on the other hand, is permitted only if it can be proved that the last move was a double step of the pawn to be captured. These two conventions lead to features unique to retrograde analysis problems.
I finally got around to reading my copy of Chess Mysteries of Sherlock Holmes: Fifty Tantalizing Problems of Chess Detection by Raymond Smullyan. I don't normally have any interest in problems, but always liked Sherlock Holmes and this book is quite entertaining. A sample dialogue between Holmes and Dr. Watson:
What about a stroll to the chess club?" Holmes remarked one early afternoon.
"Why, Holmes!" I cried in amazement. "I did not know you were a chess enthusiast!"
"Not of the conventional sort," laughed Holmes. "I do not have too much interest in chess as a game—indeed, I do not have much inclination for games in general."
"But what is chess, if not a game?" I asked in astonishment.
Holmes's face grew serious. "There are occasional chess situations, Watson, which challenge the analytic mind as fully as any which arise in real life. Moreover, I have found them as valuable as any exercises I know in developing those powers of pure deduction so essential to dealing with real-life situations."
"Tell me more," I replied with interest.
"What I have in mind, Watson, is this: In an actual game, both players have their eyes fixed entirely on the future. Each player tries to control the future in a way favor-able to his own position. Also, in most chess problems of the usual sort—White to play and mate in so many moves—the entire emphasis is on doing something to control the future. Now, although I have the deepest respect for the better problems of this sort—many of them are really ingenious works of art!—the type of strategies involved, clever as they are, is hardly of any use to me in my own work."
"I am afraid I am still in the dark," I responded.
"There are certain chessboard situations," explained Holmes, "which are of no interest to the player of chess as a game—of no interest with regard to future outcomes—but are of vital interest in providing clues as to what must have happened in the past."
For the solution see HERE.
The Retrograde Analysis Corner
Working backwards by GM Maurice Ashley- how it can help your chess