A familiar phenomenon in derivational morphology is potentiation – the creation of new contexts for some affix by the prior addition of some other affix; thus, ‑able potentiates ‑ity in English. Less familiar is the reverse phenomenon of counterpotentiation – the licensing of an affix by the subsequent addition of some other affix. In English, -al counterpotentiates -ic in forms such as whimsical, which has no counterpart in -ic without -al (*whimsic). Facilitatory relations of these two sorts reflect distinct modes of rule combination. The potentiation of an outer rule by an inner rule is a kind of rule composition in which the domain-of-definition of the composite is that of the inner rule; the counterpotentiation of an inner rule by an outer rule is a mode of rule combination in which the domain-of-definition of the combination is disjoint from that of the inner rule. Potentiation enhances conformity to the intermediate well‑formedness criterion; counterpotentiation is a deviation from this criterion.