If a datum's previous certainty factor is *CF _{p}* and a new rule computes
a certainty factor

*cfcombine(CF _{p}, CF_{n}) = *

CF _{p} + CF_{n} * (1 - CF_{p}) | CF, _{p} > 0CF _{n} > 0 |

(CF _{p} + CF_{n}) | signs differ |

/ (1 - min(| CF _{p} | , | CF_{n} |)) | |

- cfcombine(- CF _{p}, - CF_{n}) | CF, _{p} < 0CF _{n} < 0 |

This algorithm has a desirable feature: it is associative and commutative; therefore the result is independent of the order in which rules are considered.

A CF of + 1 or -1 is dominant and sets the combined CF to that value.