With the failures, a fork is a tactic which uses a part to attack at the same time at least two of the parts of the adversary, while hoping to obtain a material advantage (by the capture of one of these parts) owing to the fact that the adversary can avoid only one of the two threats. One speaks then about part taking in fork and parts taken in fork.

One distinguishes the types of fork according to the part which threatens. For example, in a fork of riding, it is a rider which attacks at least two parts of the adversary in the same blow. Any type of part of failures, even a king, is likely to take in fork, with this concerning this last which it cannot take in fork a part which will attack it, since it does not have the right to be put in failure. Any types of parts on the contrary can be taken in fork. The blow which takes in fork can itself be or not a catch.

The riding is often used for the forks and it is most frightening because none the threatened parts can take it (except if it is about another rider, but in this case the fork would hardly have direction).

The pawn S also can take in fork enemy parts: while advancing, a pawn can attack two parts in diagonal, towards the left and the right-hand side. In the diagram, the black pawn takes in fork the two white towers. (Remember that by convention the chess-board is directed with the first line of the Blacks to the top, therefore the black pawn moves downwards.)

A lady also can attack two parts at the same time, but there cannot be material profit if the two parts are not defended, or if one of the parts is not defended and the other is the unfavourable king. It is that the lady usually has more value than the parts than it attacks and it is generally no beneficial to sacrifice it. However, the possibility of a fork of lady constitutes a very real threat when the lady passed the line of the pawns, which is often the case in the ends of part. When a protected lady takes in fork the unfavourable lady and the king (or a not defended part), that can be useful to force an exchange of ladies.

The term of “royal fork” is sometimes used to indicate the situation where the king and the lady are taken in fork and it is well the worst possible fork because it follows obligatorily the loss of the lady.

When three parts or more are attacked at the same time by a rider one speaks sometimes about “fork of family”, especially (but not obligatorily) if the king is one of the parts thus threatened.

The example of fork according to is resulting from the first round of the Championnat of world FIDE of failures 2004 between Mohamed Tissir and Alexey Dreev. After the 33e blow of the white the following position is obtained:

After 33. … Cf2+ 34.Rg1 (the only legal blow) 34. … Cd3 , and the White give up. In the final position, the black rider attacks at the same time the lady and the tower black, so that after the lady will have moved, the white will lose “quality” (a tower against a minor part).

These blows are given in algebraic notation.

The forks are often used as elements of combination S which can as well utilize some others tactical.