Rules for perpetual check

Hi

Please help me with the rules for  perpetual check

A P Sukumaran

There is no rule specifically relating to perpetual check. It is a method used to force a draw, usually used when you´d otherwise lose, and occurs when a position is exactly repeated for the third time, with the same side to move. The threefold repetition rule is official, and can occur anywhere in the game (see Carlsen-Anand today, already on move 16!)

Here´s an example of perpetual check by Black to avoid being mated; he has no other option:

(Edit - I forgot the 50 move rule, thanks Fear_the_Queen!)

They can move if they are not pawns:

If there is no pawn blocking the a3-f8 diagonal then after Qa3+ the black queen get back to f8 to defend the castle position. It does not help matters either ( still mate in 2 ) but I wanted to exclude this possibility to show that the situation is absolutely hopeless for black apart from the perpetual.

In the nineteenth century, perpetual check was part of the rules. See, for example, Steinitz, The Modern Chess Instructor (1889): “When neither player can checkmate his adversary, the game is drawn. The following are instances in which this occurs:—1. By perpetual check; 2. When both players persist in repeating the same moves; 3. By stalemate; 4. When the stronger force cannot give checkmate within the number of moves specified in Law XI; 5. When the forces on either side are equal, or nearly so, as queen versus queen, rook versus rook or bishop,  etc.”

Law XI is the fifty-move rule. See http://chessskill.blogspot.com/2016/06/max-judds-draw-claim.html