Two-Prong Chess

Setup

Pieces

Rules

(2) For purpose of determining whether the "dual move" is legal, each of the two pieces moved treats the other piece as though it were still in its square of origin rather than its destination. The exception to this is Rule No. 3 below. Each piece in the dual move is considered blocked (according to normal rules) by the other piece as though it were still in its square of origin; but conversely, is not blocked by the other piece in its destination square (except that both pieces cannot have the same destination square).

(3) When a dual move is made, whether or not your king has moved into check (and hence, whether or not the move is legal) is not assessed until the entire dual-move is completed. Hence, a king can move into what would have been check, if a second piece blocks the check or captures the checking piece as part of the dual move. Any dual-move that ends with your king out of check is legal.

(4) Checkmate occurs when a king cannot be extricated from check by any single move or dual move. Stalemate occurs when a player has no legal single move or dual move.

(5) "Castling" [if part of the base game being modified by this "Two Prong" variant] is treated as a full dual-move in the "Two Prong" version of the game. One does not move a third piece.

Notes

Example: Black may not, on its first turn, move a pawn out of the way of a bishop, and then move out its bishop through the opened space.

Conversely, each piece is not blocked by the other piece on its destination square. The only exception is that both pieces may not occupy the same square.

Example: A player moves a rook and a knight as his dual move. The knight moves to what would have blocked the path of the rook; and the rook moves beyond the knight, treating it as though it did not (yet) block its path.

These principles can in theory be applied to permit any number of moves per turn with separate pieces: Three-Prong Chess, Four-Prong Chess, etc. I suspect, though, that to extend them beyond two moves per turn would be too much of a mind-bender. I once tried 4 Prong Dragonchess, and found that keeping track of the moves was cumbersome.

I feel that large chess variants (in particular) benefit from some kind of two-move, or multiple move rule, which will make them more dynamic. (This is especially so in correspondence play). With the normal one-move-per turn, the choice to move any one piece means that all other pieces on the board are paralyzed. So, whenever considerations of strategy dictate that a player focus on repeatedly moving a select number of pieces, the remaining pieces just sit doing nothing. This (it seems to me) hampers the intended "epic scope" of some large chess variants, and makes them seem less dynamic than they should be. It is also unlike the example of real armies, in which multiple units can often move independently and roughly simultaneously.

I have no opinions on what the required etiquette of physically moving both pieces should be. Perhaps a player should be required to pick up both pieces together before putting either of them in their destination squares. Alternatively, perhaps a player who has not yet moved two pieces can be thought of as still in the middle of his dual move, unless he specifies a single move by saying "done".

If castling were combined with another move (either because Rule 5 were dispensed with or because one were attempting Three-Prong Chess) then the following clarification would be necessary: Rule 3 (as always) governs whether the king is moving into check, but Rule 2 governs whether the king is moving from or through check (in which case the castling move would not be legal).

These rules have a result which some might find counter-intuitive: 2 pieces (such as a queen and rook, or a queen and pawn, or a queen and bishop) can move toward each in a dual move along the same rank, file or diagonal, and pass each other, as long as they do not reach or pass each other's square of origin. They do not collide in the middle. Anyone bothered by this can easily fashion a rule against it ("Two-Prong Chess with Collision").