On the Use of Superior Power at Decisive Points.
If a pinned piece incapable of movement or a blocked Pawn is assailed, a fight ensues on that spot, since the piece under attack under conditions as above described cannot take to flight; the only way to save the piece is by hurrying supports to it. As soon as the assailant, and were it only for a moment, obtains the superiority at the point of contest, he is at liberty to capture the piece and to hold on to the advantage thus gained. The rule by which it is determined which side has the advantage on a given spot is very simple: two pieces which dominate the spot are stronger than one and weaker than three and keep the balance to two hostile pieces on that spot. And so it is in general, even the King making no exception to this simple piece of arithmetic.