A study investigated the evolution of the use of "devil" (or as it is often spelled to represent the vernacular, divil) as part of a negation "Divil a one" (= "not a one") in Irish and Hiberno-English and traces the influence of language contact in this history. While it is found that multiple causes resulted in the development of the "devil" negation, the influences of substrate, superstrate, and universal factors are unequal. It is concluded that the principle of minimal necessity applies here: when substrate influence can be posited for the same structure in two or more language contact situations, and when this influence arises independently in at least one of the situations, the substrate is the primary causal factor in both, unless there is evidence that the structure could not have developed without a contribution from superstrate influence. contains 46 references. (Author/MSE)