*-u

Probably from pre-Germanic *-u, from Proto-Indo-European enclitic *h₂u, a clitic variant of the additive/coordinating particle *h₂o/u/i. Dunkel (2014: 334–345) compares Vedic Sanskrit उ (u) and Ancient Greek αὖ (aû), from an originally coordinative formation. The interrogative function is secondary: an additive or sentence-connecting enclitic ‘and, also, in addition’ was refunctionalized as a marker of an added, potentially alternative proposition, and then as a general polar-question marker. Dunkel explicitly compares Lühr’s (1995: 119–30) Lithuanian development, where inherited conjunctions meaning ‘or’ and ‘and’ were reanalyzed as question particles.

An alternative derivation from PIE *-we remains semantically attractive, since Gothic -𐌿 (-u)occurs in binary questions, but it is formally and morphologically less economical. Dunkel (2014: 845–48) reconstructs *-we as a separate enclitic disjunctive particle with reflexes such as Latin -ve, Vedic वा (vā), Gaulish -ue, and Ancient Greek ἤ (ḗ), all meaning ‘or’, and Tocharian B wa; deriving Proto-Germanic *-u from this particle would separate it from *-uh, which Dunkel derives from *h₂u-kʷe, and would require an additional account of the loss or remodeling of *w-.