The paper studies the semantic-pragmatic and syntactic development of the negation verb/word ei + the adverb kaas ’together, also’ into an epistemic marker and particle ega. Ega has been described as a coordinating conjunction, a marker of negation and a question word in Estonian grammars and we will show how these diverse usages come together on a timeline from the earliest written sources to present-day conversation. Ega has first been grammaticalized into a conjunction and then into an emphatic epistemic marker indicating speaker certainty as well as opposition with prior discourse. It is now being reanalyzed as a question word in cases where the negative proposition concerns matters that belong to the interlocutor’s area of competence. The study shows that inter- actional sequencing of actions may provide a crucial clue for the process of (inter)subjectification. It also proposes a novel cline of grammaticalization for a question word, and thus illustrates the benefits of combining the methods of conversation analysis and historical linguistics.