Conditional chess is a recent variant, which was invented by Joao Pedro Neto around 1996.
The rules of orthodox chess apply, with the following exceptions:
- Each turn consists of the following steps:
- White makes a normal move (A-move).
- White states a conditional move. (Below, you find explained what is a conditional move.)
- Black makes a normal move (B-move).
- Whites conditional move is executed (C-move).
- Black makes a normal move (A-move).
- Black states a conditional move. (Below, you find explained what is a conditional move.)
- White makes a normal move (B-move).
- Blacks conditional move is executed (C-move).
- The only allowed check in A-moves is when there is checkmate! If one player cannot prevent check in an A-move (and it's not checkmate), it's a draw (variant: the player loose the game).
- If there is a check in a B-move, the C-move is skipped (except if the check is cancelled by the C-move itself!) and the game returns to an A-move of the player in check (checks in B-moves aren't so great!), unless it's checkmate and then the game is over.
- There are no restrictions to C-move checks.
- If a C-move is an illegal move, it is skipped. (One possible variant: in this case, the other player can move whatever enemy piece he likes (legal move, of course) Terrible!! :-) In this variant, each game is a legal FIDE game.)
- If there is a stalemate it's a draw.
There is an exception to this general scheme in case of checks.
Conditional Moves (C-moves)
A conditional move consists of three parts: the condition, the then-move, and the else-move. The following types of conditions can be used:
- Is a specified square empty?
- Is there an enemy piece on a specified square?
- Is there a specified enemy piece on a specified square?
The then-move and the else-move are moves for the player that states the C-move. We can use the following syntax:
A C-move is executed as follows:
If condition is true, then the player makes the then-move, if not, he makes the else-move.
Here are some examples of conditions:
- a8? => is square a8 empty?
- Bg5? => An enemy bishop is in g5?
- Pe2? => An enemy pawn is in e2?
- Eg7? => There is an enemy piece in g7?
Here are some examples of conditional moves:
- d2?Nh4/e6 => If d2 is empty, then make move Nh4, else, make move e6
- Nh5?gxh5/g5 => If there is a Knight in h5, move gxh5, else, move g5.
- Pb4?Na2/Ncd3 => If there is a Pawn in b4, move Na2, else, move Ncd3.
Note: it is allowed to have a C-move with the then-move and the else-move equals. As in this case, the condition is not relevant, it is omitted from the notation, and one writes: !move. Examples of this are:
- h5?Qe2/Qe2 <=> !Qe2
- Ea1?Ra1/Rxa1 <=> !Ra1
Cristina Matos - Joao Pedro Neto (April 16, 1996)
- e4 d5
Note that 2. !d4 is planned before 1. ... d5 appears!
- ..., dxe4
- Bg5, Bg5?*Nf6*/c4
I use *...* to indicate what move was made. In 3. ... Bg5?*Nf6*/c4 black asked if there is a bishop in g5, white played 3. Bg5, so the condition is true, the then-move is executed.
- Qxd4, Be7
- Bb4?Qxb4/*Bb5*, ...
This was to prevent Bb4+.
- ..., c6
- Ba4, Ef6?Bxf6/*d5*
Using Ef6? black prevents Qxf6 and Bxf6!
- Bxf6, Bxf6
- Bf6?*Qb4*/Be5, dxe4
- Qxb7, !Qe7
White saw that he can take b7 without any problem, black will play Qe7.
- Qxa1, Bb2
- Qb2?Qxb2/Qxc3, ...
Taking the tower was an allusion. The Queen is lost! Bb2 invalidate the white C-move!
- ..., Bxa1
- Nc3, c3?Bxb2/*e3*
- fxe3, O-O
- Kg8?/*Rd1*/Nf3, Rd8
White cannot choose Rxd8 in the next move (it's an A-move!)
- Bxc6, Nd5?cxd5/*Bb2*
- Bxb2, Qxe3+
- Td1/Kxd1/e4, ...
A check in a B-move! White can move again.
- Nge2, Nc6
- Bc3?bxc3/*Rf1*, Nb4
White must protect c2, or else... (of course, black knows that :-)
- Rc1, Rc1?*Bd4*/g5
Black cannot choose Rc1?Bd4/Nc2 because of Rd2 and then Rxc2
- Rf3, Qf1+
- e3?*Rg1*/Rxe3, Bf2++
A check in an A-move, but also a checkmate!
Text by Joao Pedro Neto and Hans Bodlaender.
Last modified: April 18, 1996.