Proto-Finnic declension

The illatives of *s-stems are actually from forms like †kuninkaasen < *kuninkahe-sen with the stem in the weak grade as expected, and hence the ending in the strong grade. The long-vocalic endings -seen, -siin are by analogy to diminutives like punaiseen < *punaise-hen.

The sibilant in the conditionals has certainly been *-c-, yes. The mood marker ,has been explained to have developed from the continuative verbal suffix *-ice-, as in ilo 'joy' : iloitse- 'to revel'.

On syncope:

• I'm not sure what you mean by "contraction in the inessive". We have no evidence of any former vowel between *s and *n in the ending.
• Loss of two subsequent vowels is not attested anywhere, no. I guess the analogy of the other personal endings would have kept the 2PS potentials from contracting.
• IIUC there is no original *-te- element in the optatives: the long vowels are shaped after the relatively frequently used 3PS forms. Hence *-gotek, etc.
• I think *-ht- < *-šet- is pretty much regular, yes. Though of course this is not found in the inflection of words like hanhi or karhi where another consonant precedes. CCC contracted forms like *kante-ta- > *kantta- > *katta- 'to cover' were fossilized already by Proto-Finnic.
• Syncope before *k is exceptional and indeed does not seem to have occurred anywhere else than in nähdä, tehdä and their passives nähnyt, tehnyt. I wonder if the fact that all other -ke-stem words are back-vocalic (e.g. lukea, pukea) or nominals (e.g. mäki, väki) has something to do with this. It may also be relevant that these verbs have an exceptional inflection in Livonian, based largely on the monosyllabic stems nǟ-, tīe- (which look like as if they were from *näxə-, *texə- and not *näkə-, *tekə-).

Thank you for your answers. I meant essive not inessive, sorry about that.

For *s : *h gradation, should I apply the following rules?

• If the stem ends in -Vse- and the nominative ends in -s, then it always weakens when a vowel follows it. The following illative -s- will appear in the strong grade.
• In all other cases, the illative -s- weakens to -h-.

Would these rules give the correct inflections, or are there other considerations? What about verbs with -Vse- stems?