Glossary of Chess Problem Terms
Extracted from the documentation of Problemist, a software for solving chess problems,
written by programmer Don French

The following glossary is a brief summary of a few terms used in the discussion of chess problems. However, I strongly recommend the book, an ABC of Chess Problems, written by John Rice and published by Faber and Faber, for a more comprehensive and excellently illustrated discussion of themes and terms.

Actual play is the actual solution to the problem (as compared to the set play or virtual play or threat play). The actual play includes the key move and all legal replies. For each legal reply, there are one or more correct continuations which solve the problem. Those continuations and, if the problem is more than two moves in length, all their legal replies are included in the actual play. This continues for as many moves as the stipulated length of the problem.

A battery is formed when one piece is on the line of another piece of the same color. When the first piece moves, it uncovers the attack from the piece behind it. The first piece is called the firing piece. A battery is direct if aimed directly at the opposing King and indirect if aimed at the King's field.

A position is considered a block if a mate is set for every Black move. A position that is not a block until after the key is called an Incomplete Block, while one which is blocked before the key is call a Complete Block. A block in which the key is a waiting move is called a Waiter. If the key is a threat, the problem is known as a Block-Threat or Incomplete Block-Threat, depending upon whether the block was complete or incomplete.

A mating move that follows a Black reply and differs from the move that is set for that reply is a changed mate. See also Set Mate.

A cook is an extra, unintended, solution to a problem. The term is sometimes applied to impossible positions or ones with no solution. Occasionally, a problem will be published stipulating multiple solutions. These are intended solutions and are not considered cooks. Problems that have cooks are said to be cooked.

A Black move that counters a threat by White is known as a defense. In actual play, any defense to White's threats must create another weakness which allows White to mate.

A direct-mate is a problem in which one side, usually White, is to move and force a mate on the other side in some stipulated number of moves. Direct-mates are usually stated as White to play and mate in 2 (or 3, or 4, etc.). Sometimes they are simply stated as Mate in ..., with the unstated implication that White is to move first. The solution to a mate-in-n-moves can be defined as the one move that allows for a mate-in-n-minus-one-moves for every legal Black reply.

A dual is a choice of White moves after a Black reply. Some choose to refer to a choice of three moves as a triple and four moves as a quadruple, etc. However, the term dual can be used in all these cases. Although problems would always be better with no duals, there are degrees of offensiveness. First move duals are cooks and render the problem unsound. Duals are considered minor if both of the White moves are forced in other variations of the problem. Major duals occur when one or both of the lines cannot be compelled in any other line. Major duals thus rate more demerits than minor duals

 A helpmate is a problem where Black helps White in his mating task. In a helpmate, Black moves first and White has the task of mating in the stipulated number of moves, with Black's help at every step of the way. Black helps by making the only move that will allow White to mate in the required number of moves. See also Series Helpmate.

An ideal mate is a model mate in which every piece, Black and White, are involved in the mate. If there are Black pieces on the board other than the King, they must occupy flight squares of the Black King which are not otherwise guarded by White pieces.

Illegal force refers to a piece in a composition which could not possibly arrive at its location from a legal game of chess. A good example might be a White Bishop on a1 with a White Pawn still on b2. See also Obtrusive Force and Promoted Force. Illegal force is considered a fatal flaw in problem composition.

The squares surrounding the King.

The key of a problem is its first move. The key may be a waiting move or a move that introduces a threat. Occasionally, a key might be a checking move or a capture, but such moves require that the problem have compensating features to justify such a forceful beginning. Finding the key to a problem is the primary goal of solving it.

A problem with between eight and twelve pieces is called a Merideth, named after a nineteenth century American composer who specialized in such compositions.

Problems with fewer than eight pieces are known as a miniatures.

A minimal is a problem wherein White has only his King and one other piece.

Problems with four or fewer pieces on the board are called minimanners.

A model mate is one in which every square in the Black King's field is either occupied by a Black piece or guarded by a single White piece. Squares in the Black King's field occupied by Black pieces may not be guarded by any White piece. Furthermore, all White's pieces, with the exception of the King and Pawns, participate in the mate by guarding squares.

The term applied to a problem in which there is a complete block both before and after the key. Some or all of the set mates will be changed after the key. Also called a Block-Change.

Obtrusive force is the term applied to a piece in a problem composition that must have resulted from the promotion of a Pawn, given the assumption the position derived from a legal game of chess. However, if there are two Queens of the same color on the board, or three Knights, Bishops, or Rooks of the same color, or two same-colored Bishops on same-colored squares, the term is not applied, even though it is obvious one of the pieces resulted from a promotion. In these cases, the term promoted force is used.

A pin mate is a mate in which a Black piece that could otherwise refute the mate is pinned and therefore incapable of exercising its authority.

See Obtrusive Force.

A pure mate, like a model mate, is one in which every square in the Black King's field is guarded by only one White piece or is occupied by a Black piece. Unlike a model, however, not every White piece on the board is required to participate in the mate.

A reflexmate is a selfmate in which it is stipulated that both White and Black must give mate on the move at every opportunity. A Semi-reflexmate places the restriction only upon Black.

A refutation is a move by black that defeats a try. Refutation play is the tree of continuations that follow the try. See also Try.

The process of looking backwards in time is known as retrograde analysis. In chess problems, retrograde analysis is used to determine how a position came about, usually to determine whether an en passant capture is legal or whether castling can be disregarded as an option. It is also used to decide whether obtrusive force or illegal force is present in a position.

A selfmate is a type of problem in which White is to move in such a fashion that Black has no option but to mate him in the stipulated number of moves.

In a series helpmate, Black moves several times in a row before White delivers the mating move. The number of moves that Black makes is the stipulated number of moves in the problem.

In the original position of a problem, White may have mates that are threatened for certain Black moves. Set mates are these threatened mates. The mating play that follows the Black move is known as the set play. Often in problems, one or more set mates are changed in the post-key play.

In problems of more than two moves, there may be certain Black moves which allow White to mate in less than the required number of moves. These continuations are known as short mates.

The solution tree is the complete set of all White continuations for all Black moves at every ply of the problem. In long problems, especially where Black has numerous pieces and a lot of freedom, there may be hundreds or even thousands or tens of thousands of moves in a complete solution tree. Dual continuations for White are also a part of a complete solution tree and can add considerably to the size of the tree. The trees of moves that constitute set play, virtual play and threat play are also called solution trees.

When a piece returns to the square of its origin, the move is termed a switchback.

A threat is a mating continuation that is threatened after the key. Black is compelled to answer the threat with moves that create other weaknesses. A double threat is one that threatens two distinct mates.

The play that follows a threat is known as the threat play. Threat play is not usually realized in the actual play of a problem, since Black is typically provided with a defense to the threat. It is nevertheless interesting and can form a part of the thematic content of a problem.

A try is a near miss. It is a White attempt at a solution that fails to some Black defense. For a try to be thematic it should have a single defense and should also show the thematic play the problem was constructed to illustrate. The mating play that follows a try is known as the virtual play. The virtual play solution tree contains every continuation that leads to mate and therefore ignores the refutation. The refutation lines also constitute a tree of moves. A refutation tree consists of all the White moves that follow the refutation and the Black continuation that thwarts White's attempt at mate.

A Black move and the associated White continuation tree is called a variation. If many Black moves are followed by the same reply, these may be considered a single variation. Generally, the more variations a problem has, the better the problem.

The mating play that follows a try.

A problem in which the key move does not threaten to solve the problem. In a waiter, Black is in zugzwang, which is to say every Black move creates a new weakness that white can capitalize on. See also Block.