Training notebook · Tactics
Double check: why the king must move, and what to calculate next
In a genuine double check, two pieces attack the king at once. The legal response must be a king move. The useful training question is therefore which king destinations remain safe.
A position to work through
Calculate a candidate continuation without moving the pieces. Look for the tactical idea, consider the opponent’s reply, then compare your calculation with the recorded line.
White to move
Compare with the recorded continuation
Nf6#
This is a line from the training source, not a claim that every alternative has the same outcome. Calculate the opponent’s reply before revealing it.
Lichess CC0 puzzle database; position from Brass Pawn’s curated training data
Verify that it really is double check
One move can uncover an attack while the moving piece also checks. Confirm that both attacks reach the king legally. Do not confuse two pieces aiming near the king with two actual checks; blockers and occupied lines matter.
Because a non-king move cannot remove both checks in this situation, the defender must move the king. That move can include a king capture when the destination is safe. Saying 'the king must move' does not mean it can never capture the checking piece.
Mark escape squares before declaring mate
Inspect every neighbouring square, including the one occupied by a checking piece. A square controlled by a pinned opposing piece can still be attacked for king-move purposes under the rules; do not treat a pin as permission for your king to enter that attack.
Friendly pieces, board edges and enemy control all reduce the king's options. Count those restrictions before calculating the follow-up. A beautiful double check that gives the king an open route into safety may be less effective than an ordinary forcing check.
Use the forced response to shorten calculation
Once the legal king moves are known, calculate each branch. Some may lead to mate; another may concede material but avoid mate. Your proposed combination must survive the best of them. Do not spend time analysing irrelevant blocking or interposing moves.
From the defending side, search for the least damaging legal destination rather than emotionally rejecting all moves that look exposed. An ugly king square may be the only way to survive. The point of the motif is to narrow the legal tree, not to guarantee a winning attack.
Recognise the warning before the double check
For prevention, study the move before the double check. A king and another valuable piece aligned behind a screening piece can invite discovered threats. Exchanging that screening piece or changing the king's square may remove the idea. Do not make a defensive move without checking its tactical cost: a seemingly safe king move can enter another line. The point of backward review is to identify the warning configuration while normal choices remain, rather than waiting for the king's replies to become forced.
List every legal king destination
For four double-check positions, draw a simple list of king destinations without calculating any attacking continuation. Cross off each illegal destination and state the reason: occupied, attacked, or off the board.
Only then solve the exercise. Compare your list with the actual defensive moves. A missing legal square is a board-reading error; choosing the wrong continuation after finding all squares is a calculation error. Keep separate totals so the next training session addresses the real weakness.
Put the practice into a routine
Where Brass Pawn fits
Brass Pawn can provide tactical positions and on-device engine checking. Use the board to verify the legal king replies yourself before consulting feedback. Offline practice does not authorise using analysis assistance during an online game.