What is Empty Capture?
Kalah rule sets differ on one detail of the capture. In the standard rules played here, when your last seed lands in an empty pit on your side and the pit opposite holds seeds, you take that seed and all the seeds opposite into your store. If the pit opposite is empty, nothing happens: the seed stays where it landed and your turn ends.
With the empty-capture rule, the last seed is captured either way. When it lands in an empty pit of your own, it goes into your store together with whatever is in the pit opposite, which may be nothing. A move that ends in your own empty pit therefore always scores at least one seed.
The change is small but it alters the endgame. A lone seed sown into an empty pit no longer stays on your side to be swept up later; it scores at once and leaves the pit empty again. Tempo moves that drop a single seed into a nearby empty pit become a way to score, and counting the final sweep works out differently.
Rule changes
| Rule | Standard Mancala | Empty Capture |
|---|---|---|
| Capturing | Standard MancalaYour last seed lands in an empty pit of your own and the pit opposite holds seeds: take both into your store. | Empty CaptureThe same when the pit opposite holds seeds. |
| Pit opposite is empty | Standard MancalaNo capture. The seed stays in your pit and your turn ends. | Empty CaptureThe last seed is still captured: it goes to your store on its own, and your turn ends. |
| Scoring | Standard MancalaSeeds stay on your side until captured or swept up at the end. | Empty CaptureSingle seeds can be banked straight away by ending a move in an empty pit of your own. |
| Everything else | Standard MancalaFour seeds per pit, anticlockwise sowing, extra turns in your store, the end-of-game sweep. | Empty CaptureThe same, with any seed count from 3 to 6. |
History
Kalah was patented and sold in the United States by William Julius Champion, Jr. in the 1950s. Several variations of its rules are in use, and the empty-capture rule is one of them; others sow clockwise, change how the seeds left at the end are counted, or replace captures with sowing on from the landing pit.
The empty-capture rules are the ones used in the first computer solution of the game. Geoffrey Irving, Jeroen Donkers and Jos Uiterwijk published Solving Kalah in the ICGA Journal in 2000, showing that with perfect play the first player wins the four-seed game by 10 and the five-seed game by 12. The six-seed game was shown to be a first-player win in 2011 by Anders Carstensen, and later analysis by Mark Rawlings put the margin at just 2 seeds.