For the volitional, if the verb begins with a vowel, insert an h before switching vowels: adnedu 'I add it' --> ahednedu 'I add it on purpose'.

Does that mean that the verb es'u 'to not be' is irregular? In the conjugation table, it forms its volitional as eves'u and not as ehes'u.

The first explanation I came up with is that verbs like 'to be' and 'to do' tend to be irregular in many languages. But perhaps a better one is this: according to the lexicon, it derives from Methaiun wech-, and the v in the volitional may be a reflex of the Methaiun w (similar to how some stems change their consonants in, say, Verdurian due to the underlying consonant in the Cadhinor word).

Of the vowel-initial verbs I found in the lexicon, this is the only one whose original form starts with a consonant, which probably accounts for this irregularity. Do you perhaps want to state that reason somewhere? :-)

Cheers,
Philip.