[...] "final particles", the most common of which is "en" "already, now, finished".
- Zwicky (2004), Pag. 366

Still more types of particles occurr only in main clauses. These include a set of "initial particles", some modal in meaning [...], most functioning as sentence connectives; a set of "modal particles", intervening between the clause temporal and the subject, and again acting both as modals [...] and as connectives [...]; and a collection of "final particles" beside those that can occurr in both main and embedded clauses. These final particles mark questions and imperatives of various types, emphatic assertions and denial, and bewilderment or surprise. [...] But there is no reason to think the final and initial particles are anything other than words: adverbs, in fact.
- Zwicky (2004), Pag. 367