Whether you call it a combination, a sacrifice, a manoeuvre, or a forced variation, it's an essential part of the game. * * *
Ask a few chess players why they play, and you're bound to get a variety of answers. One says "for the competition"; another says, "to keep my thinking processes in shape;" and yet another says, "for the beauty". That last answer may raise some eyebrows. What could possibly be beautiful about moving little wooden pieces on a chequered board?
Chess, in fact, has very little to do with little wooden pieces. It is more the manipulation of complex geometric patterns to achieve a definite goal. These patterns take many forms and vary according to the ingenuity and skills of the players.
One of the most fertile areas of beautiful patterns is the combination. Combinations are one of the things that are easy to spot, but hard to define. Emmanuel Lasker defined them as a net of variations.
In the rare instances that the player can detect a variation or net of them which leads to a desirable issue by force, the totality of these variations and their logical connections, their structure, are named a 'combination.' And he who follows in his play such a chain of moves is said to "make a combination."
Siegbert Tarrasch offered specific advice for the middle game:
"The strategic conduct of the Middle Game generally arises out of the Opening. Frequently one of the players has secured a slight advantage in the Opening and this must be further developed in the Middle Game. Often the pawn formation shows the direction the attack is to take. In chess, to play correctly, we can never do what we wish, we must do only what we are forced to do, what the position demands."