The Optative mood is a volitive mood that signals wishing or hoping, as in English I wish I might, or I wish you could, etc.
The athematic Optative has an alternating suffix -ie / -i (zero-grade), while the Thematic has one regular -oi. Secondary endings are used to form the Optative.
NOTE. The thematic suffix is normally considered to be the athematic one added to the thematic vowel -o-.