Let’s finish the sound changes between protolanguage 0 and 1 by adding some vowel loss. This will help with some synchronic features – justifying the forms of the personal suffixes and adding some interest to verb conjugation.
I’ve already established that word-final vowel loss happens between protolanguage 0 and protolanguage 1. This explains why an affix that shows up as prefixed /si-/ shows up as suffixed /-s/ and not /-si/. However, there’s a bit of a problem with that. Protolanguage 0 permitted words to end in consonants. That means, that if you have a root like /xat-/, and you suffix the ending /-da/, after vowel loss it’ll become /xatd/, which is extremely noncompliant with the phonotactics of protolanguage 1. We can insert the epenthetic vowel /a/ to clear up this issue, making /xat-da/ become /xatad/. This change will make long vowels short, rather than deleting them, and it will also happen before the disappearance of /h/ and /ʔ/, giving a contrast between word-final consonants, short vowels and long vowels.
However, that’s not the only vowel loss I want to implement. I really like verb roots that start with CCV in this language. However, to do that, right now you need a verb that starts with VCCV by default, which won’t be too common. However, we can get more CCV roots by generating them from CVCV. I’ll therefore make this rule:
V[-long] → ∅ / _ CVV // $ _, $ C _, CC _
In other words, short vowels are deleted in syllables directly before long vowels, if it wouldn’t cause an illegal syllable structure. I’ll also say that when an /i/ dissappears this way after an alveolar or velar obstruent, it’ll palatalize it:
{t,k}, {d,g}, {s,x}, {z,ɣ} i → tɕ, dʑ, ɕ, ʑ / _ CVV // $ _, $ C _, CC _
Combine these changes with the voiced obstruent shifts in languages 1a and 1b, and this produces some very interesting divergent forms:
/gitaːb/ → /gitaːb/ → /kitɑːv/, /ɣitɜːp/
/si-gitaːb/ → /sidʑkaːb/ → /siʝtɑːv/, /sitʃtɜːp/
I’ll also add a similar rule for vowels in syllables after long vowels, though there won’t be any palatalization occurring here:
V[-long,-stress] → ∅ / VVC _ // _ CC, _ C $
(I added the stress exception so that the prefix diː- and other prefixes with long vowels can’t trigger this in the stem.)
In practical terms, this means that every verb will have a maximum of three principal parts – one for when they only take a prefix, one for when they only take a suffix, and one for when they take both. (There’s no situation in this language where a verb takes no prefix or suffix.) Not every verb will have all of them, so I picture an English-like situation, where only as many as are necessary will be listed in the dictionary.
This may not truly be the end to the sound changes between protolanguage 0 and protolanguage 1, as they are looking far too similar for my liking still. But this is enough to go off of right now – we can back-implement other sound changes later. Next time, I’ll return to verb agreement. But this time, we’re looking at protolanguage 0 again, and seeing how its system of verb agreement evolved into the one in protolanguage 1.