Underpromotion

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This article uses algebraic notation to describe chess moves.

In chess, underpromotion is promotion of a pawn that has reached the eighth rank to any piece other than a queen; that is a rook, a bishop or a knight. It is uncommon, since the queen is the most powerful piece, but can be necessary in specific situations. In the 2006 ChessBase database of 3,200,000 games, the breakdown of games in which promotions occur (counting games in which multiple promotions of the same type by the same player occur only once) is approximately:

• queen - 96.9%
• knight - 1.8%
• rook - 1.1%
• bishop - 0.2%

The frequency of truly significant underpromotions is, however, smaller than this (see Insignificant underpromotions below).

Contents 1 Promotion to a knight 2 Promotion to rook or bishop 3 Insignificant underpromotions 4 See also 5 External links

[edit] Promotion to a knight

Since the knight moves in a way which the queen cannot, knight underpromotions can be very useful, and are the most common type of underpromotion.

In the top diagram on the right, promoting to a queen is only a draw (with 1.e8=Q causing stalemate), but 1.e8=N+! instead wins by virtue of a fork: 1... Kf8 2. Nxc7, and bishop and knight against king is a forced mate.

Promotion to knight may also be done for defensive reasons; to the right is such a case. Black threatens ...Bd4# and 1.e8=Q merely delays the mate by two moves. White draws with 1.e8=N!, guarding the f6 square, thus enabling White to meet to 1...Bd4+ with 2.Bf6. Note that even after 1...Bf7, 2.Bf6 is still possible, since the ending of two bishops versus one bishop (after 2... Bxe8) is a theoretical draw.

Tim Krabbé points out (scroll down to No. 242) that Zurakhov-Koblentz (pictured in the diagrams at left and right) furnishes a very rare example of a game with two "serious" underpromotions to knight. In the position at left, Black threatens 57...Nxg7, and if White avoided this by promoting to queen, rook, or bishop, Black would reach a drawn position with 57...Ne7+! and 58...Nxg8. The only winning move is 57.g8(N)! Krabbé notes that this is a rare example of a non-checking knight-promotion.

Twenty-one moves later, the players reached the position at right. Once again, a promotion to anything other than a knight would be a blunder allowing a knight fork, e.g. 79.c8(Q)?? Nd6+ and 80...Nxc8, with a drawn ending. White instead played 79.c8(N)+! (Here, there are other winning moves, such as 78.Kc5.) Kb8 80.Kb6 and Black resigned, since White cannot be stopped from promoting a third pawn -- this time to a queen.

[edit] Promotion to rook or bishop

Because the powers of the rook and the bishop are combined in the queen, there is usually little reason to underpromote to them, but this too can be necessary sometimes. The most common cases involve avoiding stalemate:

In the position at left (with White to move), Black threatens to capture White's pawn, and a promotion to queen would be stalemate. Only 1.g8(R)! wins.

At right is a position from a recent game at the Irish championship [1]. Here too, a promotion to queen would allow stalemate: 70...b1(Q)?? 71.Qh3+! Kxh3 stalemate. Instead, the game concluded 70...b1(R)! 0-1

In the position at left,(scroll down to No. 243) Black decided to promote the c-pawn in order to deflect White's queen, thus allowing ...Qe5+. However, 49...c1(Q)?? or c1(R)?? would stalemate White's king, allowing a draw by 50.Rxg7+! followed by Qg5+. Instead, Black played 49...c1(B) 50.Qxc1 Qe5+ 51.Kg1 Qg3+ 52.Kf1 Bd3+ 0-1

Less often, underpromotion to bishop or rook may be necessary not to avoid stalemate, but to induce it and thus save a draw in an otherwise hopeless position. To the right is an example from the end of a study by Herman Mattison.

Both king moves lose quickly (they can be met by ...Rgg7, for example), so the pawn must be promoted. 6.b8=Q and 6.b8=R both lose to a capture on c8, and 6.b8=N, while leaving a stalemate after 6...Rgxc8??, loses quickly after 6...Rcxc8. This only leaves 6.b8=B!: since the c7 rook is now pinned, Black must either lose it with a theoretical draw or play 6...Rgxc8 which, with a bishop on b8 rather than a queen or rook, is stalemate.

Underpromotion to knight or rook in practical play is rare, and to bishop is even rarer, but in composed chess problems such as this last example, it occurs more often. Perhaps the most famous example is the Saavedra position. Some cases can be quite spectacular: a study by Jan Rusinek, for example, sees White promoting to knight, bishop and rook in order to induce stalemate. An Allumwandlung is a problem where promotions to all four possible pieces occur. An extreme example is the Babson task, where underpromotions by black are countered by matching underpromotions by white (so if black promotes to a rook, so does white, and so on), white's underpromotions being the only way to mate black in the stipulated number of moves.

[edit] Insignificant underpromotions

A majority of underpromotions in practical play are, as Tim Krabbé puts it, "silly jokes" -- underpromotions made where there is no real need to do so. A recent high-level example was the game Shirov-Kramnik, Amber Blindfold, 2005. In the position shown to the left, Black played 25...e1B+. This underpromotion has absolutely no significance since 25...e1Q+ would work just as well; either move forces 26.Qxe1.

[edit] See also

• Lasker Trap - an opening trap which features an underpromotion on the 7th move.
• Promotion (chess)

[edit] External links

• Examples of underpromotion in practical play from Tim Krabbé