In diachronic comparison of languages, say PIE to Latin to
Romance, it is a classic recognition that the later languages
strictly lose some of the morphologically marked categories. PIE
had 8 noun cases (nominative, accusative, genitive, etc), Latin
5, Romance 2 or even 1. Pick a morphological category and pretty
much always the complexity is reduced: past participles in
English are more likely to become weak rather than strong, the
subjunctive is disappearing, there's no grammatical gender at
all. Presumably those forms (that were later lost) came from
somewhere, those categories and phonological markers were
created. I can imagine a cycle of inflected to isolating (a
period of loss) and then back to inflectional where the
grammatical markers get phonologically assimilated (fused onto
the root), but i have no data to support this. I feel like I
heard a long time ago that Finnish/Hungarian/Turkish might be
gaining distinctions or that the word initial inflections in
verbs in Irish came from phonological inter