In this article, I conduct a quantitative analysis of do absence in negative declaratives in the present tense in a dialect from the north-east of Scotland, Buckie. Analysis of nearly 800 contexts of use reveals that this variation is entirely conditioned by linguistic internal constraints. The most significant of these is person and number of the subject — 3rd person singular subjects and plural NPs have no do absence, while do is variable in the remaining pronouns. I argue that a syntactic explanation best accounts for this patterning of use. Where there is no overt - s inflection in the present tense (influenced by the “northern subject rule”), do is not obligatory in Buckie Scots. Frequency effects, lexical restrictions and processing constraints are called upon to account for the range of frequencies of do absence seen in the variable contexts. Lastly, there is no significant change in use of do across three generations of speakers, highlighting the community members’ relative immunity to prescriptive norms.