On the Vedic -si Imperatives, the Celtic Subjunctive and the Prospective

In Vedic there are some athematic forms in -si used as 2nd sg. imperative (not indicative!); comparable forms are to be found in Old Irish, Tocharian and Hittite. The existence of semi-thematic sigmatic subjunctives or futures in other Indo-European languages implies the reconstruction of an athematic s-paradigm which underwent a shift to modal values since early date in the protolanguage.