This article investigates word order changes in negated periphrastic constructions in the history of Basque. A number of linguistic variables are argued to correlate with these changes: the negative particle ez is increasingly focalized in main clauses, the innovative pattern negative particle – auxiliary verb – main verb allows for more syntactic flexibility than the conservative one, and the word order changes do not progress at equal rates in all clause subtypes. Genre issues are also considered, including the hypothesis that the loss of the conservative order main verb – negative particle – auxiliary verb of main clauses occurs first in texts close to oral language. Moreover, it is argued that eastern dialects are more innovative than western dialects and that efforts towards standardization of the language have slowed down this case of word order change.