The Opposition

What you are up against

There is no material here and nothing to capture. Kings may not stand next to each other, and that single rule is the entire game. You want to reach the far rank; Black wants to keep you off it for ever. Black does not have to win anything, only to prevent something, which is a much easier job and is why a lone king can hold a whole rank at all.

It looks like a race and it is not one. Count the moves and you are seven ranks from home with a king that covers three squares of the rank you want. Walk straight at it and you will find yourself stopped a rank short every time, shuffling sideways while Black shuffles with you.

How it knows

The verdict under the board is not an opinion. The position is small enough to solve outright: sixty four squares for each king and two sides to move is eight thousand states, which a browser works through in about a fortieth of a second. Every one of them is scored with the number of moves it takes White to get home against the best defence, and the table is checked against its own definition at every legal position by a test.

So the game can tell you that a move threw the win away the moment you make it, rather than three moves later when you are wondering what went wrong. Being marked is not the same as being taught, and the difference is entirely in how soon you are told.

Black uses the same table. It plays the move that holds out longest, so a lost defence is still a real one, and it will not wander into a hole to be polite.

Solving it outright also settles how much the opposition really explains, which is a fair question to ask of any rule of thumb. Of the three thousand odd positions with White to move, Black can hold ninety six of them, and Black has the opposition in every single one. Not most. All of them. That is as strong a statement as the idea could hope for, and it is checked by a test rather than asserted.

The converse is not true, and the board does not pretend it is. The eighth rank is eight squares wide and one king often cannot cover enough of it, so plenty of positions are won with the opposition against you. Having it is what Black needs to hold, not what White needs to win. This starting position is the knife edge, chosen because on it the two coincide exactly: take the opposition and you get through, fail to and you never do.