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| rowspan="2" | '''Candidate passed pawn''',<br/>
a [[Pawn|pawn]] on a [[Half-open fileFile|half-open file]], which, if the board had only pawns on it, would eventually become a [[Passed Pawn|passed pawn]] by moving forward. Whereas this definition is obvious for a human, in a form presented above it would require no less than a separate [[Recursion|recursive]] search routine. For that reason, computers have to use approximations of that rule.
One possibility is to define a pawn as a candidate, if no square on its path is controlled by more enemy pawns than own pawns. However, this simple heuristics rules out an early recognition of a candidate passed pawns. For example with white pawns on a4 and b5 and black pawn on a7, the b5 pawn would be viewed as a candidate passer only after a4-a5.
