Reconstruction:Proto-Finnic/-pi

Etymology
Related to. The final *-i may be of the same origin as in (see ).

Lauri Hakulinen, in his seminal Suomen kielen rakenne ja kehitys, proposes a sound change from unstressed final *a to *i in bisyllabic words with a long initial syllable or any word with more than two syllables. This could then have been generalized by analogy (and participles exempted likewise by analogy, as their oblique forms would not have been affected).

Kallio (SUST264) discusses the same sound change and shows that it has also taken place in the comparative ending,, as well as the instrumental derivative suffix and superlative ending, , and the caritive suffix,.

Originally restricted to 'Coastal Finnic' (i.e. Finnic except South Estonian), but has also spread into some South Estonian dialects. The original South Estonian third-person singular forms were endingless, which is probably an archaism rather than an innovation.