Not Promoting in Tsume Shogi: Why Narazu Is Sometimes the Answer
Hiroki Obara · Developer
When a tsume shogi answer says 不成, “not promoting”, it can come as a surprise. Promotion makes a piece stronger, so why would you turn it down? Many people who have just learned shogi promote every time a piece enters the enemy camp, just to be safe.
This post covers why declining promotion, narazu, is the correct move in some tsume shogi problems. Once you see how a piece’s moves change when it promotes, narazu stops looking strange and starts looking natural. The basic promotion rules are in Shogi Promotion and Drops, so here I stick to how it works in mating problems.
Pieces that lose something when they promote
Promoted pieces fall into two groups. The rook becomes a dragon and the bishop becomes a horse. Each keeps all of its moves and adds the king’s one-step moves. Nothing is lost.
The silver, knight, lance and pawn all move like a gold once promoted. The pawn only gains moves. But the silver, knight and lance each have a move the gold does not.
- Silver: moves diagonally backwards. A gold cannot.
- Knight: jumps two squares forward and one to the side. A gold cannot jump.
- Lance: moves any distance straight forward. A gold moves only one square forward.
These three lose something when they promote. In tsume shogi, narazu is usually the answer when the move they would lose is the one the mate needs. How the pieces move is in How Shogi Pieces Move.
In the two positions below, the move given is the only mate, and promoting does not mate.
Position 1: keeping the silver’s backward diagonal
Position 1: Defender’s king on 1二, lance on 1一, silver on 2二, pawns on 1三 and 2三. Your silver on 3二 and knight on 3三. Nothing in hand. Mate in 1.
The answer is silver to 2一 without promoting, ▲2一銀不成. The silver moves diagonally forward from 3二 to 2一.
An unpromoted silver on 2一 covers 1二, diagonally behind it. That is check. Around the king, the lance on 1一, the silver on 2二 and the pawns on 1三 and 2三 all belong to the defender, so the king cannot move to any of them. It cannot take the silver on 2一 either, because your knight on 3三 covers 2一. The defender’s silver on 2二 moves diagonally backwards to 1一 and 3一, so it cannot reach 2一 either. That is mate.
What about ▲2一銀成, promoting? A promoted silver moves like a gold. From 2一 it covers 1一 and 3一 to the sides and 2二 behind, but not 1二 diagonally behind. There is no check. Every attacking move in tsume shogi must be a check, so this move is not even a candidate.
The silver moved forward here, but the check came from its backward diagonal. Narazu with a silver appears when you need that backward diagonal. If the king sits diagonally behind the square your silver can promote on, put the unpromoted move on your list.
Position 2: keeping the knight’s jump
Position 2: Defender’s king on 1一, knight on 2一, bishop on 2二, lance on 1二. Your knight on 3五. Nothing in hand. Mate in 1.
The answer is knight to 2三 without promoting, ▲2三桂不成. From 2三 an unpromoted knight jumps to 1一 and 3一, so it checks the king on 1一.
The king’s squares, 2一, 1二 and 2二, are all filled with its own pieces. A knight’s check cannot be blocked. And no defending piece can take the knight on 2三. The bishop on 2二 moves only diagonally, so it does not cover 2三 straight below it. That is mate. A king smothered by its own pieces and mated by a knight: chess players will recognise this as a smothered mate.
After ▲2三桂成, the promoted knight moves like a gold. It covers 1二, 2二 and 3二, but not 1一. No check.
A knight can only stay unpromoted in certain places. On the first and second ranks it would never be able to move again, so it must promote there. Knight narazu only comes up when the knight lands on the third rank.
Bishop and rook narazu: avoiding uchifuzume
A bishop or rook loses nothing by promoting, so there is never a reason to decline promotion to keep a move. Yet there are tsume problems where an unpromoted bishop or rook is the answer. Most of them have to do with uchifuzume.
Uchifuzume is the foul of mating with a pawn dropped from hand. If a dropped pawn gives check and the king has no way out at all, you are not allowed to drop it.
When a bishop becomes a horse or a rook becomes a dragon, it covers more squares. If that extra coverage takes away the king’s last escape square, then a later pawn drop leaves the king with nowhere to go, and the drop becomes illegal. If the piece stays unpromoted, one escape square is left open, so the pawn drop is legal. The king steps onto that square, and another piece mates it there.
So an unpromoted bishop or rook is a deliberate choice to cover less and leave the king a way out. You keep the piece weaker so that the pawn drop is allowed. A pawn also gains coverage when it promotes, so when pawn narazu is the answer, you can read it the same way, looking for a reason not to add coverage. The details of uchifuzume are in Uchifuzume Explained.
Where promotion is compulsory
When you think about narazu, you also need to know where you cannot stay unpromoted. Under the Japan Shogi Association’s game rules, a piece with no further moves is a foul. You cannot leave a piece unpromoted on a square from which it could never move again.
- A pawn or lance must promote on the first rank.
- A knight must promote on the first or second rank.
The silver, bishop and rook have no such restriction. They can stay unpromoted even on the first rank. The silver in Position 1 is unpromoted on 2一, on the first rank. More on this in Fouls in Shogi.
Breaking the “always promote” habit
One fix is to ask the same two questions every time a promotion is possible.
First, if the piece is a silver, knight or lance: what does it lose by promoting? The backward diagonal, the jump, or the long reach forward. Check whether that move is giving check or covering an escape square.
Second, if the piece is a bishop, rook or pawn: what does the extra coverage block? If your plan includes a pawn drop on the far side of that square, check that it won’t become uchifuzume.
When you can’t find the answer to a tsume problem, it’s worth asking whether you only read the promoting moves. When you list candidates, list “promote” and “don’t promote” as two separate moves. That alone should cut down the times you get stuck on a narazu problem.
How 不成 is written in solutions is in How to Read Tsume Shogi Solutions.
Chess underpromotion
Chess has a similar idea. When a pawn reaches the last rank, there are positions where a rook or knight is right and a queen is wrong. A queen can cover so much that the opponent is stalemated, or a knight can give a check no queen can. A stronger piece getting in the way is the same idea as narazu. I wrote about it in Underpromotion.
Playing narazu in Shogi365
Shogi365 is a tsume shogi app with four levels: Easy is 3-move mates, Medium 5-move, Hard 7-move and Expert 9-move, with 1,000 problems each. Some problems have narazu in the solution.
When you make a move that can promote, the app asks “Promote?” and you choose “Promote” or “Don’t promote”. On a square where the piece would have no further moves, it promotes without asking. In the move list, a move that could have promoted but didn’t is marked 不成.
The setting “Ask before promoting” starts out on. If you turn it off, a piece always promotes when it can. Then you can no longer play the unpromoted move in a narazu problem, so leave it on.
Moves that are not checks cannot be played. In Position 1 or 2, choosing “Promote” gives no check, so the app shows “That move is not a check.” and the board stays as it was. It doesn’t count as a failure. Any check, right or wrong, can be played, and the defender answers automatically with the reply that lasts longest. If you don’t mate within the move count, the attempt fails, and you have three retries.
A hint lights up the piece and the square for the next correct move. You still make the move yourself, so whether to promote is your call. If the lit square is inside the enemy camp, consider the unpromoted move too. After solving, Review lets you step back and forward one move at a time.
All problems are free to solve. The app shows ads, and a one-time Remove Ads purchase turns them off. How to use the app is in Getting Started with Shogi365.
