Andernach (Fairy Chess) – color-changing rule
Andernach
Definition
Andernach (often called Andernach chess or the Andernach condition) is a classic fairy chess condition in which every capturing piece immediately changes color at the end of its move. In standard usage, kings are exempt: a king may capture but does not change color. The rule applies to all other pieces, including pawns. This single twist creates rich tactical paradoxes, deep retrograde puzzles, and striking problem themes.
Andernach is primarily used in Fairy chess compositions rather than over-the-board play. It is named after the town of Andernach, Germany, renowned for regular gatherings of problemists where many fairy ideas were discussed and developed.
Core Rules and Conventions
How it works
- On any capture, the capturing piece (except the king) changes color when the move finishes.
- The move must be legal in the final position. That means if your capture would leave your own king in check from the newly flipped piece, the move is illegal.
- Pawns that change color reverse their direction of movement and promotion side accordingly.
- Promotion: a pawn promotes on the last rank associated with its current color at the time it arrives there.
- En passant: a pawn capturing en passant also changes color (as it is a capture).
- Castling: unchanged by the condition; however, a rook that has flipped color is no longer your rook and cannot be used for castling.
- Check and mate are judged in the final position after any flip has occurred.
Notation and clarity
Algebraic notation is used as usual, but composers often annotate a capture that flips color with a reminder (e.g., “And.” or “Andernach”) in commentary. Keep in mind that the piece delivering the capture will belong to the opponent in the diagrammed final position of that move.
How It Is Used in Chess
In compositions and studies
Andernach is a fertile condition for problemists. It enables ideas that are impossible in orthodox chess, such as:
- Interference and self-block motifs, where a capture deliberately flips a piece to the opponent to block their own lines.
- Color-changing switchbacks that realize themes like Switchback, Phoenix, and Pronkin.
- Complex helpmates, selfmates, and seriesmovers that rely on controlled color-flips to arrange mating nets.
- Retrograde analysis and Proof game tasks, where composers count necessary color-changes to prove legality.
- High-theme tasks like AUW (AUW; Allumwandlung) and even Babson-like relationships (see Babson task), made plausible by the extra freedom of changing sides mid-solution.
Over-the-board and variants
While rarely played OTB, Andernach is a well-known “condition” in the fairy community and often combined with other conditions such as Circe or Madrasi to amplify paradoxes.
Strategic and Thematic Significance
Why it’s interesting
- Self-interference: A capture can donate a defender to your opponent on a critical square, creating novel blocking and line-closing ideas.
- Deflection and decoy: A capture can “steal” a piece by changing its team and its duties, realizing Decoy, Deflection, and Interference in unusual ways.
- King safety paradoxes: Some seemingly natural captures are illegal because the flipped piece would then check your own king.
- Pawn geometry: Reversing direction mid-journey lets problemists choreograph multi-phase promotions and color-specific promotion tasks.
Examples
1) Pawn flip demonstration (toy example)
Start from the initial position. Consider the moves 1. e4 d5 2. exd5. In Andernach, after 2. exd5 the pawn that captured on d5 changes color and becomes a black pawn on d5. It will now move downward on Black’s future turns. This simple flip already changes middlegame plans dramatically.
Try this short sequence for visualization (note: the viewer shows orthodox moves; use the text above to imagine the color-flip after 2. exd5):
2) Self-block by flipping a piece
Position (visualize a simplified setup):
- White: Kg1, Qe2, Re1, Bc4, pawns g2, h2
- Black: Kg8, Re7, Be7, pawns g7, h7
Idea: White wants to attack along the e-file but the black rook on e7 defends. In Andernach, 1. Bxe7! flips the bishop to Black on e7, paradoxically increasing congestion on e7. With two black pieces clogging the file, lines get closed and new tactical resources appear (e.g., White may later aim at deflections or discover a mating net with heavy pieces). In orthodox chess, this capture simply exchanges; in Andernach, it reorganizes guard duties via self-blocking.
3) Promotion direction reversal
Position (sketch): White pawn on d5, Black pawn on e6. If White plays 1. dxe6 (capturing the e6-pawn), that pawn becomes Black on e6 and now moves down the board. If Black later plays …e5-e4 and manages to advance that flipped pawn, it can promote on the first rank for Black (from White’s perspective), creating promotion tasks impossible in orthodox play. Composers exploit this to realize Allumwandlung and color-dependent promotion cycles.
4) Legality pitfall
In Andernach, a capture that would, after flipping, cause your own king to be in check is illegal. For example, if your rook on e1 could capture a piece on e7, but the final position would leave your king on e1 checked by that rook now belonging to Black on e7, the move is not allowed.
History and Trivia
Background
The condition is named after Andernach, a German town famous for long-running meetings of chess problemists and fairy-chess enthusiasts. The Andernach gatherings helped popularize many “condition”-based ideas. Over decades, Andernach has become one of the most recognizable labels in fairy chess, akin to Circe or Madrasi in household status among problemists.
Interesting notes
- Because flipping happens at move completion, a capture cannot use the capturing piece to give check to the opposing king in the final position—after all, it no longer belongs to the mover!
- Composers often combine Andernach with rebirth rules (e.g., Circe and Anti-Circe) to create spectacular cyclical effects.
- The condition is a favorite in Seriesmover genres and helpmates, where precise control of color-changes is the main artistry.
Related Variants and Combinations
Common relatives
- SuperAndernach: Pieces change color on every move (capturing or not).
- Anti-Andernach: Pieces change color on non-capturing moves; capturing moves do not flip color.
- Madrasi: Opposing like pieces mutually paralyze when attacking each other; combining with Andernach produces rich paralysis/flip cycles.
- Circe/Anti-Circe: Rebirth-on-capture rules; with Andernach, the order and effect of rebirth and flipping are specified by the problem’s convention.
Designers frequently cite classic themes—Interference sacrifice, Decoy sacrifice, Deflection sacrifice, Line opening/closing, Switchback, and even Phoenix/Pronkin realizations—made possible or enhanced by Andernach’s color-change mechanism.
Practical Tips and Pitfalls
Working with the condition
- Always check king safety after a capture: the flipped piece might now attack your own king.
- Track pawn direction carefully. A single flip completely changes its path, capture squares, and promotion side.
- In solutions, mark turning points where color flips enable/disable lines to help readers follow the logic.
- When combining with other conditions, state the convention clearly (e.g., flip timing vs. rebirth timing in Circe-type problems).
Quick Demonstration PGN
Illustrative mini-sequence
Use this just to visualize piece travel; remember: in Andernach the capturing piece flips color at the end of its capture.
See Also
FAQ
Do kings flip color on capture?
By standard convention, no. Kings may capture, but they do not change color. Some problem statements may specify a different rule, but the default excludes the king.
Is a capture legal if the flipped piece would check my own king?
No. All legality is judged in the final position. If your capture results in your king being in check by the now-opponent piece, the move is illegal.
How is en passant handled?
It is a capture; therefore, the capturing pawn flips color at the end of the move. The usual conditions for en passant must still be satisfied.
Where does a flipped pawn promote?
On the last rank of its current color’s side at the moment it reaches promotion, which may differ from its original side if it has flipped earlier.