They come in pairs
The attempt to categorize the combinations in search for new patterns already revealed an interesting point. We usually think of combinations as an infinite way to combine tactical themes. But in practice, they usually come in pairs. If you have a double attack/fork, there are two targets involved. That can be pieces, or another tactical theme. For instance: piece + piece piece + mate threat example piece + loading a battery (discovered attack) example piece + invasion example There are about 18 common used tactical themes: Preliminary moves Attraction/magnet Blocking Capture/replace target Clearance Coercion/Chase Distraction/Overloading Interference Quiet Move Zwischenzug Duple attack or trap Discovered Attack Fork/Double Attack Invasion Mate threat Pin Promotion/advanced pawn Removal of the guard Skewer/X-Ray Attack Trapped Piece These 18 themes can combine with each other in 18 x 18 = 324 ways. In practice, not every combin...