That Hittite denominatives in a ( i ) correspond to IE verbs in -āyō is supported by etymologies ( ) and by agreement with Latin in method of formation (cf. aestuāre but piscārī ) from u- and i -stems. In Hittite no ā -stems have been recognized, the suffix is therefore not a conglomerate. This adds new interest to the fact that in IE (esp. Rig Veda and Homer) many -āyō verbs have no corresponding ā -stem. Probably the IE ā -stems are largely ‘backformations’ patterned on a number of ā -stems that were (cf. Hirt) simply dissyllabic bases.
E. H. Sturtevant (Fri,) studied this question.