Тай сёги: Крупнейший вариант японских шахмат

25x25 grid variant of Japanese chess
Tai shogi (泰将棋 tai shōgi or 無上泰将棋 mujō tai shōgi "grand chess", renamed from 無上大将棋 mujō dai shōgi "supreme chess" to avoid confusion with 大将棋 dai shōgi) is a large board variant of shogi (Japanese chess). The game dates to the 15th century and is based on earlier large board shogi games. Before the discovery of taikyoku shogi in 1997, tai shogi was believed to be the largest playable chess variant, if not board game, ever. One game may be played over several long sessions and require each player to make over a thousand moves. It was never a popular game; indeed, a single production of six game sets in the early 17th century was a notable event. Like other large board variants, but unlike standard shogi, the game is played without drops, and uses a promotion by capture rule. Because of the terse and often incomplete wording of the historical sources for the large shogi variants, except for chu shogi and to a lesser extent dai shogi (which were at some points of time the most prestigious forms of shogi being played), the historical rules of tai shogi are not clear. Different sources often differ significantly in the moves attributed to the pieces, and the degree of contradiction (summarised below with the listing of most known alternative moves) is such that it is likely impossible to reconstruct the "true historical rules" with any degree of certainty, if there ever was such a thing. It is not clear if the game was ever played much historically, as the few sets that were made seem to have been intended only for display.

Tai shogi is essentially a merger of two other large board shogi variants: dai dai shogi and maka dai dai shogi. Almost all the pieces of those two smaller games are included, and where the same pieces are found, they move the same way. Additionally, many of the tai shogi pieces not from those two games already appear in the even more popular chu shogi. Only nine extra pieces are added that do not appear in any smaller games – the peacock, soldier, vermillion sparrow, turtle snake, side dragon, golden deer, silver hare, fierce eagle, and ram's head soldier. (Indeed, two of the Edo era sources generally do not describe a piece for tai shogi if it exists in a smaller variant.) The promotion rule is contested. Dai dai shogi and maka dai dai shogi have very different promotion rules. The promotion rules given on the Japanese Wikipedia are similar to those of maka dai dai shogi: almost all pieces promote, but most to the lowly gold general, even if they are much more powerful; and many weak pieces turn into "free" versions of themselves (in which stepping moves are replaced by unlimited ranging moves in the same directions). However, the promotion rules given in English language sources are similar to those of dai dai shogi: most pieces do not promote. Both agree that promotion is compulsory upon capture if the piece can promote. In maka dai dai shogi with its demotions, The Chess Variant Pages suggest that promotion is only compulsory when capturing a promoted piece, which seems more reasonable because otherwise the most powerful pieces would quickly disappear. However, in tai shogi non promoting copies of those powerful pieces can be obtained by promoting some weak pieces. The difference is unusual: in all smaller variants, Japanese Wikipedia agrees with the English language sources on promotions, even though it does not always agree on the moves. There are additionally some confusions in the Japanese Wikipedia promotions: for example, the fragrant elephant is said to exist in tai shogi, but without a piece promoting into it. Because of this, the promotions from the English language sources have been followed throughout this article, with alternatives given in the footnotes. That is, most pieces do not promote, and promotion (if possible) is compulsory on capture.

The objective of the game is to capture the opponent's emperor and prince (or princes). When the last of these is captured, the game ends. There are no rules for check or checkmate; however, in practice a player resigns when checkmated.

A player may not make a move if the resulting position is one that has previously occurred in the game with the same player to move. This is called repetition (千日手 sennichite). Note that certain pieces have the ability to pass in certain situations (lions, lion dogs, furious fiends, soaring eagles, horned falcons, teaching kings, and Buddhist spirits). Such a pass move leaves the position unchanged, but it does not violate the repetition rule, as it will now be the turn of the other player to move. Of course, two consecutive passes are not possible, as the first player will see the same position as before. However, evidence from chu shogi problems suggests that this at least does not apply to a player who is in check or whose pieces are attacked, as otherwise one could win via perpetual check or perpetual pursuit. The modern chu shogi rule as applied by the Japanese Chu Shogi Association (JCSA) is as follows, and presumably tai shogi should be similar. If one side is making attacks on other pieces (however futile) with his moves in the repeat cycle, and the other is not, the attacking side must deviate, while in case of checking the checker must deviate regardless of whether the checked side attacks other pieces. In the case of consecutive passes, the side passing first must deviate, making turn passing to avoid zugzwang pointless if the opponent is in a position where he can pass his turn too. Only the fourth repetition is forbidden by these rules. If none of these are applicable, repetition is a draw.

When a player makes a move such that the opponent's emperor or prince (sole one in play) could be captured on the following move, the move is said to give check to the emperor or prince; the emperor or prince is said to be in check. If a player's emperor or prince is in check and no legal move by that player will get the emperor or prince out of check, the checking move is also a mate, and effectively wins the game. If a player has both an emperor and one or more princes in play, then the player need not move only one out of check. Recall that an emperor can only capture a royal piece if that royal piece is unprotected. (Capturing non royal protected pieces is legal, just almost always a very poor move.) This prohibition applies even if the opponent's last royal piece is being captured: here "protected" means that the opponent could recapture if we ignore that he has just lost his last royal.

A player who captures the opponent's sole remaining king or prince wins the game. Thus a player who is checkmated or stalemated will lose. In practice this rarely happens; a player will resign when loss is inevitable and the king will be taken on the opponent's next move (as in International Chess) because of the tradition that it is seen as an embarrassment to lose. The very artificial situation of a smothered stalemate, where no moves are possible (even those that would expose the king), is not covered in the historical sources. On their pages for chu shogi and dai shogi, The Chess Variant Pages rule this as a loss for the stalemated player, for definiteness. A player who makes an illegal move loses immediately. (This rule may be relaxed in casual games.) There is a (probably facetious) rule that draws cannot be agreed.

The method used in English language texts to express shogi moves was established by George Hodges in 1976. It is derived from the algebraic notation used for chess, but differs in several respects. Modifications have been made for tai shogi. A typical example is P 8h. The first letter represents the piece moved (see above). Promoted pieces have a + added in front of the letter. (e. g., +CC for a wizard stork (promoted Chinese cock). The designation of the piece is followed by a symbol indicating the type of move: for an ordinary move or x for a capture. Next is the designation for the square on which the piece lands. This consists of a number representing the file and a lowercase letter representing the rank, with 1a being the top right corner (as seen from Black's point of view) and 25y being the bottom left corner. (This method of designating squares is based on Japanese convention, which, however, uses Japanese numerals instead of letters. For example, the square 2c is denoted by 2三 in Japanese.) If a soaring eagle, horned falcon, lion or Buddhist spirit captures by 'igui’, the square of the piece being captured is used instead of the destination square, and this is preceded by the symbol '!'. If a double capture is made, then it is added after the first capture. If a capture mandates the player to promote the piece, then a + is added to the end to signify that the promotion was taken. For example, ORx7c+ indicates an old rat capturing on 7c and promoting. In cases where the above notation would be ambiguous, the designation of the start square is added after the designation for the piece in order to make clear which piece is meant. Moves are commonly numbered as in chess.

These descriptions are taken from Japanese Wikipedia, which references the Edo era publications 象戯図式 Shōgi Zushiki (SZ), 諸象戯図式 Sho Shōgi Zushiki (SSZ), and 象棋六種之図式 Shōgi Rokushu no Zushiki (SRZ). The first two are generally though not always in agreement, but the third differs in the case of most pieces which are not found in smaller shogi variants. For reasons of space, and to avoid duplication, issues regarding pieces that already appear in dai dai or maka dai dai shogi are discussed in those articles rather than here.