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This page is written by the game's inventor, João Neto.

Conditional chess

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:

  1. Each turn consists of the following steps:
    1. White makes a normal move (A-move).
    2. White states a conditional move. (Below, you find explained what is a conditional move.)
    3. Black makes a normal move (B-move).
    4. Whites conditional move is executed (C-move).
    5. Black makes a normal move (A-move).
    6. Black states a conditional move. (Below, you find explained what is a conditional move.)
    7. White makes a normal move (B-move).
    8. Blacks conditional move is executed (C-move).

    There is an exception to this general scheme in case of checks.

  2. Checks:
    1. 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).
    2. 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.
    3. There are no restrictions to C-move checks.
  3. 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.)
  4. If there is a stalemate it's a draw.

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:

The then-move and the else-move are moves for the player that states the C-move. We can use the following syntax:

syntax: condition?then-move/else-move

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:

Here are some examples of conditional moves:

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:

Sample game

Cristina Matos - Joao Pedro Neto (April 16, 1996)

  1. e4 d5
  2. !d4

Note that 2. !d4 is planned before 1. ... d5 appears!

  1. ..., dxe4
  2. 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.

  1. Qxd4, Be7
  2. Bb4?Qxb4/*Bb5*, ...

This was to prevent Bb4+.

  1. ..., c6
  2. Ba4, Ef6?Bxf6/*d5*

Using Ef6? black prevents Qxf6 and Bxf6!

  1. Bxf6, Bxf6
  2. Bf6?*Qb4*/Be5, dxe4
  3. Qxb7, !Qe7

White saw that he can take b7 without any problem, black will play Qe7.

  1. Qxa1, Bb2
  2. Qb2?Qxb2/Qxc3, ...

Taking the tower was an allusion. The Queen is lost! Bb2 invalidate the white C-move!

  1. ..., Bxa1
  2. Nc3, c3?Bxb2/*e3*
  3. fxe3, O-O
  4. Kg8?/*Rd1*/Nf3, Rd8

White cannot choose Rxd8 in the next move (it's an A-move!)

  1. Bxc6, Nd5?cxd5/*Bb2*
  2. Bxb2, Qxe3+
  3. Td1/Kxd1/e4, ...

A check in a B-move! White can move again.

  1. Nge2, Nc6
  2. Bc3?bxc3/*Rf1*, Nb4

White must protect c2, or else... (of course, black knows that :-)

  1. Rc1, Rc1?*Bd4*/g5

Black cannot choose Rc1?Bd4/Nc2 because of Rd2 and then Rxc2

  1. Rf3, Qf1+
  2. 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.