Today, I’ve been thinking about verbs in Engadinese — what forms should they have?
I had a look at Romansh verbs and the Latin origins, to see what kind of sound changes happened in the endings, to give me some ideas. Then I wrote down Greek endings and thought about what kind of endings those verbs could have in Engadinese.
I decided that -ον (and -εν) endings would disappear just as with nouns, and -ω for first person singular present indicative would also go, as in Romansh. I also did a bit of regularising with contract verbs and their thematic vowels.
Now the most difficult question is how regular to make things. Ancient Greek did some pretty irregular things in some places, such as -μι verbs, second aorists, deponent verbs, etc. etc.
Romansh (at least, Rumantsch Grischun) did quite a bit of levelling: even if the stems are irregular, the endings are nearly always regular. For example, in the present indicative of esser “to be”, essan “we are” and essas “you are” are regular (or nearly so; the endings are those of non-present tenses), and the other TAM forms (imperfect, subjunctive, and conditional) are perfectly regular in terms of endings (-a -as -a -an -as -an for impf. and subj., -0 -as -0 -an -as -an for cond.) and irregular only in terms of the stems (er- sai- fiss- rather than the expected essev- essi- essiss-).
So I’ll have to think what to do with ειμή, δίδωμι, etc. etc.: how much regularity to preserve.
I think Modern Greek can be a small guide; it’s preserved quite a few alternate stems, but has tended to regularise endings. (For example, only one set of active aorist endings rather than two; first person singular is always -α rather than -(σ)α or -ον depending on the kind of aorist; and the conjugation of είναι looks more like the present/imperfect indicative of a middle verb.)
Speaking of which, synthetic middle and passive voice will probably disappear, à la Latin > Romance, to be replaced by auxiliary + participle.
And the conditional will probably be formed from the aorist optative (compare pluperfect subjunctive for Romansh), and the subjunctive from the present optative (since the present subjunctive sounds nearly exactly like the present indicative after Ancient-to-Byzantine Greek sound changes merging -ει and -η as well as -ο and -ω).