Andernach Chess - Fairy-Chess Definition

Andernach Chess

Definition

Andernach Chess is a fairy-chess condition (i.e., a set of rules that deviates from orthodox chess and is mainly used in composed problems) whose distinguishing feature is that every capturing piece, except the kings, immediately changes colour after the capture. In other words, a white bishop that takes a black knight becomes a black bishop on the square of capture, now owned and controlled by Black; conversely, a black rook that captures a white pawn turns into a white rook.

Main Rules

The kings retain their colour for the whole game and never switch sides, even if they capture.
All other pieces (queen, rook, bishop, knight, pawn) switch colour on the completion of a capture, before check and mate are evaluated.
En passant, promotion, castling, stalemate, and the fifty-move rule all follow orthodox practice, except that colour-changes after captures may alter who is to move or who is in check.
The side making the capture is credited with the taken material, even though the capturing piece “defects” to the opponent.

How It Is Used

Andernach Chess is almost exclusively employed in composition (studies, help-mates, self-mates, proof games, etc.), where the colour-flip produces paradoxical positions and striking tactical motifs that cannot occur in orthodox play. While casual over-the-board games are possible, the condition is best appreciated as a creative laboratory for problemists.

Strategic & Tactical Significance

Timed Defection: A piece may intentionally capture in order to switch sides, e.g., a white rook might take a black pawn on g7, turn black, and instantly give check to the white king on g1.
Self-Blocking & Self-Pinning: A newly-flipped piece can obstruct its original army’s lines or pin its former comrades, a fertile theme for help-mates.
Promotion Dynamics: If a pawn promotes by capture (e.g., exd8=Q), the newly-born piece also changes colour, potentially creating a powerful piece for the opponent.
Tempo Play: Since every capture not only removes a unit but also adds one to the opposing side, material imbalances can oscillate wildly; sometimes the best move is to avoid capturing.

Historical Background

The condition is named after the German town of Andernach, where it was introduced during a problem-solving meeting in 1993. It quickly gained popularity in fairy-chess magazines such as Schach-Report and Feenschach, spawning sister variants like Anti-Andernach (pieces switch colour when making non-capturing moves) and Super-Andernach (kings change colour as well, though still only one king can be in check at a time).

Illustrative Mini-Example

Position (FEN): 8/8/8/8/5k2/8/4P3/6K1 w - - 0 1

1. e3xf4 B
- White’s pawn on e3 captures the black knight on f4 and turns black; it now sits on f4 as a Black pawn.
- Because it is Black’s piece, the side to move becomes Black.
1… g5xf4 w
- Black’s pawn on g5 captures the new black pawn on f4, turning white and giving check to the original Black king on f4! A single square has switched allegiances twice in two moves.

Full Problem Example — Help-Mate in 2

Composer: Manfred Rittirsch, 1994
Stipulation: h#2, Andernach (Both sides cooperate so that Black is checkmated on White’s second move.)

Explanation:

1. Bb5xa4 w — Black’s bishop from b5 captures its own pawn on a4, becomes a white bishop and now pins the black king on e5 along the diagonal.
1… Ke5f5 — The pinned king steps onto f5, cooperating.
2. B4d7 w — The reborn white bishop vacates a4, guarding e6.
2… Bf5e6# — The original black dark-squared bishop (still black) mates its own king with the help of the white-turned bishop. A distinctive Andernach flavour emerges because colour changes create the mating net.

Interesting Facts & Anecdotes

The first published Andernach problem (K. Bedoni, 1993) featured a spectacular quadruple colour-change on the same square in just three moves.
Some computer engines (e.g., the fairy-chess engine Fairy-Stockfish) explicitly support Andernach mode, allowing problemists to test ideas rapidly.
Because captures can create extra defenders for the opponent, the condition beautifully embodies the “be careful what you capture” principle—an extreme form of the 19th-century aphorism, “Every move creates a weakness.”
The variant also provides a didactic lesson in evaluation: material count alone is unreliable when every exchange instantaneously flips one piece to the other side.