Introduction to retros

What are retros?

Behold a simple chess position.

White is in check, but is it mate? A little reflection will lead you to answer “Aha! If white can take dxc6 en passant then it’s not mate, otherwise it is. But you need to tell me if …c7-c5 is the last move.”

Well, what if I told you that you could deduce that by yourself, simply based on the position?

Such is a retrograde analysis problem. The goal could be anything stipulated by the composer; the method to getting the answer will involve logical reasoning, armed with only¹ the rules of chess, and the knowledge that the position must have arisen from a legal game of chess (however silly the moves are).

If you’re reading this page you’re probably already curious about retros, but if you’re not then here are a few more to show what crazy things one might be able to prove:

You can deduce the last 10 single moves (5 times of black move-white move) leading to the diagram, including the identity of captured pieces (if any).

Again, you can deduce the last 11 single moves, after you figure out which units are white’s and which are black’s!

You can prove that this is a draw by the 50-move rule! In other words, you can definitively show that at least the last 50 white and 50 black moves were not captures nor pawn moves.

OK, how do I solve these retros then?

Solving retros is all about logical reasoning. It’s a skill that can be learnt, but isn’t easily explained in just a few paragraphs. Writing full solutions for each retro would take many words to fully lay out, even with the background knowledge in place – but after getting a little experience solving, we never really need that level of detail.

For now, there is an excellent introductory article by Nikolai Beluhov, who is himself an outstanding composer of retros. Through many thoroughly explained examples and exercises, you can discover and acquire the skills needed to solve retros yourself.

On this site, I will likewise attempt to give an introduction to this art, and eventually prepare you to understand the solutions to the problems presented above.