Chess Problems: The Half-pin Theme

8/31/2012 – When two chess pieces are half-pinned against the king, and one of them moves, the other becomes fully pinned – that is the "half-pin" theme in problem chess. It combines well with many other themes and motifs, providing fertile ground for composers for well over a century. Our problem expert David Friedgood explains the idea with two introductory problems, and gives us two more to solve.

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Chess Problems: The Half-pin Theme

By David Friedgood

The concept of the half-pin is quite simple: “Two units are said to be half-pinned [against the king] when one of them becomes completely pinned when the other moves.” (John Rice, “Chess Wizardry: The New ABC of Chess Problems”, B.T. Batsford 1996). The half-pin theme intensifies the richness of the solving experience. It combines well with many other themes and motifs, providing fertile ground for composers for well over a century.

[Event "Good Companions"] [Site "?"] [Date "1921.??.??"] [Round "?"] [White "K.A.K. Larsen"] [Black "Mate in 2"] [Result "*"] [Annotator "Friedgood,David"] [SetUp "1"] [FEN "R4b2/1Kp3p1/8/1kN5/8/1r6/NnQ5/1R6 w - - 0 1"] [PlyCount "3"] [EventDate "1921.??.??"] 1. Nd3 {Threatening 2.Qc6#. The thematic variations are: 1...} Nc4 {(continued in main line)} (1... Rc3 2. Qa4# {The move of the rook has opened the way for the queen to mate, depending on the fact that the black knight is now pinned and has lost control of a4.}) ({Non-thematic variations are:} 1... c5 2. Qxb3# {taking advantage of the interference of the bishop by the pawn, which stops it from interposing on b4.}) (1... Bc5 2. Qxc5#) 2. Nc3# {Depending on the fact that Black's rook is now pinned by the Rb1 and also by the self-blocking of c4, allowing the knight to interfere with the queen in delivering mate.} *

The first problem is a simple introduction. The half-pin structure is already visible on the b-file: when the black rook or knight moves off this file the other becomes pinned by the b1 rook. All we have to do to activate the half-pin variations is to find the key move that will provoke the thematic defences.

The second problem shows a masterly treatment by a great exponent, combining the half-pin with self-block, line-opening, interference, and unpin.

[Event "1st Prize Hampshire Telegraph and Post"] [Site "?"] [Date "1919.??.??"] [Round "?"] [White "Comins Mansfield"] [Black "Mate in 2"] [Result "*"] [Annotator "Friedgood,David"] [SetUp "1"] [FEN "8/8/2P1Q3/B2R4/r1k1n2r/pNn4p/B1qP3K/N1R2b2 w - - 0 1"] [PlyCount "3"] [EventDate "1919.??.??"] {The good key is} 1. Qf5 $1 {paradoxically giving up the Q+R battery pointing at Black's king in order to cover b5 in preparation for the threat 2.Rd4#. The thematic variations involve defences by the half-pinned pieces on c2 and c3: 1. ..} Ne2 {protecting d4 makes no less than 3 "defensive errors": it causes Black's queen to become pinned, unpins the Pd2, and interferes with the Bf1, all of which are necessary to enable White to mate by...(continued as main line)} (1... Nxd5 {is the next defence, this time making just one defensive error in addition to the pinning of the black queen: the self-blocking of the d5 square, enabling the white queen to release control of it in order to mate by} 2. Qxf1#) (1... Nb5 {is our third thematic defense, this time the additional error being the self-blocking of b5. Now the bishop+knight battery can open and deliver mate by} 2. Nc5# {self-interfering with the rook. The clever point here is that the knight had only c5 and d4 to choose between, all other destinations being occupied by friendly forces. d4 would have been the wrong choice, as it would have interfered with the rook's control of d3 and provided the black king with a flight square.}) (1... Qd3 {is the queen's single thematic defence, and it shows the other side of the coin to 1...Nb5. Now the c3 knight becomes pinned, losing control of the B+N battery, and this time the queen self-blocks on d3, enabling the knight to choose the d4 square rather than c5 as its destination:} 2. Nd4#) ({Non-thematic defences include:} 1... Qxd2+ 2. Nxd2# {with mate by double-check}) (1... Qxb3 2. Bxb3#) ({Any move of the e4 knight defends by opening the line of the rook on h4 to the d4 square, but this unguards c5 as well as opening the line of the queen to protect d3, allowing e.g.} 1... Ng5 2. Rc5#) 2. d3# *

The last two diagrams are for the reader to solve. In each case, you have to find the unique key move for White, after which Black is unable to avoid mate on the second move regardless of what the defender plays. In both cases the half-pin is easy to spot and the variations are relatively simple, but the keys are quite crafty. As a hint to the inexperienced solver, I would mention that the key of a problem does not necessarily carry a threat.

Mate in two moves

Mate in two moves

Solutions will appear in approximately one week.

Any queries or constructive comments can be addressed to the author at

Copyright in this article David Friedgood 2012/ChessBase

The British Chess Problem Society (BCPS), founded in 1918, is the world's oldest chess problem society. It exists to promote the knowledge and enjoyment of chess compositions, and membership is open to chess enthusiasts in all countries.

The Society produces two bi-monthly magazines, The Problemist and The Problemist Supplement (the latter catering for beginners), which are issued to all members. Composers from all over the world send their problems and studies to compete in the tourneys run by the society.

The BCPS also organises the annual British Chess Solving Championship, and selects the Great Britain squad for the World Chess Solving Championship. The Society holds an annual residential weekend, with a full programme of solving and composing tourneys and lectures; this event attracts an international participation. Members are also entitled to use the resources of the BCPS library, and the Society book service, which can provide new and second-hand publications.

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