Friday, October 17, 2014

Counting Checks and Calculating Replies

When calculating forcing moves you often have to consider checks -- how many do you (or your opponent) have on the board, and how might your opponent reply.  This is very basic, but sometimes it is helpful to reiterate the fundamentals.

First, to count the number of checks it is important to know the maximum number of possible checks each piece can give regardless of the actual position.

Rooks – (almost) always two:

  • A Rook on a1 trying to attack h8, can move to either a8 or h1.
  • The pattern will look like a square/rectangle, and the two squares will always be ON the board.
  • Find both squares.
  • If the Rook is already on the same file/rank as the target, it can only have 1.
Bishops/Knights – usually two:

  • Bishop and knights can only attack (in one move) targets on the same color.
  • The Bishop pattern will look like a diamond, and often one of the two squares will be off the board.
  • Knights depend on color AND proximity. A knight must have four or less files/ranks between itself and the target.
Queens – no more than 12:
  • Look for three squares on the rank, file, and both diagonals.  Sometimes the squares will be off the board.
  • Like the Bishop, the Queen depends on color. If the target is on the opposite color, the Queen can only have two squares on the diagonals instead of three.
Queens by far are the hardest. Always look for three squares on all four lines (rank, file, and two diagonals). I find it easiest to look at along the four lines going out from the target.

Pawns -- maximum of two (one each on the adjacent files)

That gives a maximum of 24 checks (4 from two Rooks, 2 from one Bishop on the same color, 4 from two Knights, 2 from two Pawns, and 12 from one Queen).  

Usually you won't have that many because your knight might be too far away, or you might only have one bishop and the enemy king is on the other color square.  But I find knowing these numbers helps you find ALL possible checks!  

A second very basic but very important issue is the six different kinds of checks.  Some offer the opponent fewer options – and are therefore more forcing – than others:
  1. Regular checks – allows your opponent all three replies (capture, block, or move) and is therefore the LEAST forcing.
  2. Knight checks – cannot be blocked. More forcing than regular checks.
  3. In-your-face checks – cannot be blocked. More forcing than regular checks.
  4. Discovered checks – allows your opponent all three replies. More forcing because of the secondary threat created by the leading piece.
  5. Capture-checks – allow your opponent all three replies. More forcing because your opponent has to reckon with the loss of material. (Even better is when the ‘capture-check’ is also ‘in-your-face’).
  6. Double checks – allows only one option – to move the king.
Basic stuff, but extremely important to have engrained in your chess DNA.

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