Jishogi or Impasse

Some games can last a very long time, and both players may come to believe that it is impossible to checkmate the opponent. For these reasons, there are alternative ways to end the game besides a normal win. This section does not refer to losses due to illegal moves or improper conduct, nor to repetitions, but exclusively to Jishogi, or Impasse. This situation can lead either to a replay of the game, with Sente and Gote swapped, or to a win. Please note that a formal drawn game does not exist in shogi.

Referring to the Official Rules (Article 9) of the Nihon Shogi Renmei, the alternative ways to conclude a game are mainly 3 plus 1.

To identify them, one must consider the interplay of multiple conditions. The main ones are: the belief that checkmate is impossible, Nyūgyoku or Ainyūgyoku (one or both Kings having entered), and the number of moves. Other conditions follow from the combination of the above.

First of all, we need to define Nyūgyoku: Osho or Gyokusho is in the promotion zone, that is, the last three ranks from its starting side.

From this it follows that Ainyūgyoku occurs when: Osho and Gyokusho are both in the promotion zone.

Note: the difference between Nyūgyoku and Ainyūgyoku is important.

The verification of the interpretation of Article 9 was shared on Reddit. I thank everyone who has contributed, and will contribute, to clarifying this.

The fundamental conditions

1. The move number (often implied) may seem secondary, but in reality it can be the factor that distinguishes one method from another;
2. Considering it impossible to conclude the game by checkmate (in one case this is not required);
3. Agreement between the players, or a declaration by a single player;
4. Nyūgyoku and or Ainyūgyoku.

The conditions and the examples are explanations, not literal translations of the Rules. Four theoretical examples follow to better explain how the official rules are applied.

Theoretical examples

Example 1 – with agreement

1. the game is at move n<500 (tacit assumptions, see example 3);
2. both players consider it impossible to end the game by checkmate;
3. one player is in a Nyūgyoku position, or both are in an Ainyūgyoku position;
4. the two players agree to Jishogi (Impasse);
5. all pieces are counted, except Osho or Gyokusho, on the shogiban and in the komadai as if they were unpromoted;
6. Hisha and Kakugyo are worth 5 points, all other pieces are worth 1;
7.1 if a player has fewer than 24 points, they lose the game;
7.2 if both players have at least 24 points each, the game must be replayed.

Example 2 – with declaration

1. the game is at move n<500 (tacit assumptions, see example 3);
2. one player is in a Nyūgyoku position, not in check, and with at least 10 other pieces in the promotion zone;
3. the player in a Nyūgyoku position does not reach an agreement with the opponent and, before completing their turn, makes the declaration;
4. all of the declarer’s pieces that are in the promotion zone and in their own komadai are counted (no other pieces are counted, Osho or Gyokusho are not counted);
5.1 if the declarer has at least 31 points, they win;
5.2 if the declarer has between 24 and 30 points, the game must be replayed;
5.3 if the declarer fails to meet even one condition, they lose.

Example 3 – at move 500

1. if no agreement is reached and the game reaches 500 moves;
2.1 if neither player is in check, the game is stopped and must be replayed;
2.2 if a player is in check, one must wait until the checking sequence ends, then the game is stopped and replayed;
3. no one can win.

Example 4 – 27 point rule

1. in an amateur tournament, the 27 point rule must be provided for in the Tournament Regulations;
2. it must be specified whether the 27 point rule leads to a replay of the game or to a win for Gote;
3. one player is in a Nyūgyoku position, or both are in an Ainyūgyoku position;
4. both players have 27 points each;
5. the two players agree to invoke the 27 point rule;
6. the replay or Gote’s win is determined by the Tournament Regulations (Sente cannot win in any case).

(quote)

“…

【第9条】入玉

第1項
入玉とは、一方の玉が敵陣に入った状態をいう。

第2項
相入玉は、双方の玉が入玉した状態をいう。

第3項
入玉または相入玉において、どちらも相手の玉を詰ます見込みがなくなった場合、第4項または第5項の対応を行う

…”