Alice Chess

~417.31 ppm

C. van Gog, 05 April 2022

"Alice in Wonderland", an oil painting by Marie-Eleonore Godefroid
Source: Dall-E.

Alice chess is a wonderful chess variant invented by V. R. Parton. Wikipedia mentions 1953 as the year of the invention but does not give a source. After looking around for a little bit, I stumbled upon the wonderful pamphlet “Chess—Curiouser and Curiouser” written by none other than V. R. Parton himself.

In the present cuboid, my concern is quite simple. I am trying to find an answer to the question “What are the rules of Alice chess”? At first sight, the answer seems irrelevant. But as we shall see, there is some controversy. Here is what the Chess Variants Pages tell us:

The standard game of Alice Chess is played using two boards, A and B. All pieces move as in standard chess. The normal array is on board A; board B starts empty.

The rules are amazingly simple. In turn, each player makes a single move on either board following these three rules:

  1. A move must be legal on the board where it is played.
  2. A piece can only move or capture if the corresponding destination square on the other board is vacant.
  3. After moving, the piece is transferred to the corresponding square on the other board.

But what about castling and capturing en passant? Here the opinions diverge. I will argue that the answer flows naturally and unambiguously from the essence of the rules of chess. This is an essentialist point of view, but that is okay since we are practicing what Parton calls “Scacetic philosophy”!

Castling

This is easy: there is no reason to abolish castling since castling is perfectly possible within Alice chess. Player castle following all the usual rules on Board A (Rule 1) and then the rook and king are transported to Board B (Rule 3). Castling is not allowed if one of the destination squares is occupied (Rule 2) or if the king ends up in check on Board B. Since Caïssa has gracefully allowed denizens to castle in chess, they have the same liberty in Alice chess. (Quite unlike No Castling chess and No Castling Alice chess.)

En passant

Here is where Alice chess gets tricky. Many great minds have stumbled upon the en passant question, or even given up by abandoning the rule altogether. To find the scacetically determined rule, we need to understand the essence of en passant. This term translates to “in passing”: a pawn that is on its way to move two squares gets ambushed and captured by a nearby enemy pawn. It may look like it reached its destination square before capture, but that is just an illusion—it never made it further than one square!

What is the equivalent in Alice chess? Despite the feverish discussions on this point on the Worldwide Web, the answer is surprisingly simple. En passant is only possible if both pawns are on Board A! Why is that? Well, the captured pawn needs to be on Board A for sure, as that is the home of their starting rank. What about the enemy pawn? For concreteness, let us say there is a white pawn on d2(A) and a black pawn on e4(A) and the white pawn attempts to move from d2(A) to d4(A) after which it transfers to the empty square d4(B).

But in its perilous journey from d2(A) to d4(A) it crosses the treacherous square of d3(A) and gets ambushed by the black pawn on e4(A)! This pawn captures its white counterpart and then transfers to the empty d3(B)! This is how en passant works in Alice chess! It is also perfectly aligned with Rule 1, since capturing e.p. works the same as in chess: we just need to verify that the transfer square d3(B) is empty (Rule 3).

Ignoramuses uneducated in Scacetic philosophy claim Some people claim that a black pawn on e4(B) could also capture the white pawn en passant, but this is illogical. The white pawn safely reaches its destination square d4(B) without ever passing by d3(B)! There is no way for e4(B) to prepare an ambush. Indeed, d3(B) might very well be occupied by another piece! The square d3(B) has nothing to do with the movement of e2(A). The fact that e2(A) could have landed there if it moved one square forward only is beside the point.

It should be noted that the logic of ambushing a piece is not arbitrary. This logic lies at the basis of both the usual rules for castling in chess and Rule 1 of Alice chess. A king may not pass through a square under attack while castling precisely because it would get ambushed and captured on its way! If capturing kings were allowed in chess, the king would get captured en passant in such a case! The same logic also explains why a king may not step into check before transferring to the other board (Rule 1).

Conclusion

The rules are clear. Alice chess is a gorgeous game.