Combination

A forcing variation that uses tactical elements to exploit special conditions in the position and achieve a particular goal. A sacrifice usually goes with a combination and is its characteristic sign.

Conditions and purpose

The special conditions may consist of: the enemy king's exposure to mate or perpetual check; undefended pieces, or the chance for a weaker piece to attack a stronger one; a far-advanced passed pawn; or having almost none of your own pieces able to move (stalemate combinations).

These special conditions let the side carrying out the combination choose a line that uses at least two tactical elements (double attack, pin, and others). This line is forcing, since every move either creates a threat or meets one.

The goal of a combination can be to deliver mate or stalemate, to gain a material or positional advantage, to repel the opponent's attack, to ease one's defense, and the like.

A sacrifice — voluntarily handing the opponent a material advantage — is almost always part of a combination.

Aesthetics

A combination captures the most essential elements of chess beauty. Its aesthetic effect rests on originality (surprise), purposefulness, logic (it grows out of the whole course of the play), and complexity (length, numerous branches). A combination is more beautiful when forcing moves alternate with quiet ones that create no obvious threats.