Wikipedia explains how the Inflectional Phrase has a VP as its complement and an NP (the subject of the phrase) as its specifier. It is long ago that I studied this, but a quick look at Sprachliches Wissen by Grewendorf confirms it. And the analysis works alright for many languages.
So I am unsure of how we can account for cases like the following Welsh sentence:
Naeth a dyn brynu car did the man buy car 'The man bought a car'
I can't figure out where the IP even is. Is
naeth the complement of the IP? Then why is it to the left of the subject? Or has
naeth somehow moved to the complementiser slot? Then why is it getting conjugated?
Either way, I would love to see some syntax trees of entire sentences for Welsh and maybe other VSO languages.