The auxiliary do (tun) is one of the most-discussed constructions in West Germanic. In German, there is a striking opposition between modern standard German, where the construction is virtually ungrammatical and considered to be "sub-standard" by most speakers, whilst, as this book shows, the construction is attested in all modern dialects as well as historic stages since 1350. In answering why auxiliary tun is ungrammatical in modern standard German,...