The Universe of Discourse

Fri, 27 Mar 2020

Last week Pierre-Françoys Brousseau and I invented a nice chess variant that I've never seen before. The main idea is: two pieces can be on the same square. Sometimes when you try to make a drastic change to the rules, what you get fails completely. This one seemed to work okay. We played a game and it was fun.

Specfically, our rules say:

1. All pieces move and capture the same as in standard chess, except:

2. Up to two pieces may occupy the same square.

3. A piece may move into an occupied square, but not through it.

4. A piece moving into a square occupied by a piece of the opposite color has the option to capture it or to share the square.

5. Pieces of opposite colors sharing a square do not threaten one another.

6. A piece moving into a square occupied by two pieces of the opposite color may capture either, but not both.

7. Castling is permitted, but only under the same circumstances as standard chess. Pieces moved during castling must move to empty squares.

Miscellaneous notes

Pierre-Françoys says he wishes that more than two pieces could share a square. I think it could be confusing. (Also, with the chess set we had, more than two did not really fit within the physical confines of the squares.)

Similarly, I proposed the castling rule because I thought it would be less confusing. And I did not like the idea that you could castle on the first move of the game.

The role of pawns is very different than in standard chess. In this variant, you cannot stop a pawn from advancing by blocking it with another pawn.

Usually when you have the chance to capture an enemy piece that is alone on its square you will want to do that, rather than move your own piece into its square to share space. But it is not hard to imagine that in rare circumstances you might want to pick a nonviolent approach, perhaps to avoid a stalemate.

The name “Pauli Chess”, is inspired by the Pauli exclusion principle, which says that no more than two electrons can occupy the same atomic orbital.