Affix counterposition has two subcases: in the first (exemplified by the inflection of reflexive verbs in Lithuanian), an affix that is suffixed to the stem in some words is suffixed to a prefix in others; in the second, mirror-image case (exemplified by Noon adjective concord), an affix that is prefixed to the stem in some words is prefixed to a suffix in others. Rule aggregation models the phenomenon of affix counterposition as a deviation from the stem operand criterion involving a rule of affixation R whose operand is ordinarily a stem (when R isn’t aggregated) but is instead an affix (when R is aggregated to the rule introducing that affix). Rule aggregation brings affix counterposition into conformity with the affix directionality criterion. Nevertheless, there are real deviations from the latter criterion: some languages have true ambifixes that actually function as prefixes in some word forms but as suffixes in others. Gurma noun-class inflection exemplifies this possibility. Moreover, the morphotactics of Italian pronominal affixes involves a significant interaction between true ambifixation and rule aggregation.