In this Government & Binding Theory book I'm reading, it is assumed that "to" in to-infinitives corresponds to verb inflection, meaning that in x-bar tree "to" appears under INFL, exactly where one puts "tense" markers (i.e. the suffix -ed).
What I don't quite follow in this assumption is that "to" is not a suffix and it is not a tense, so I fail to see why it would be associated with "verb inflection" in x-bar theory. Then again, if you don't put "to" under INFL, where would you put it? But is that sufficient grounds for saying that "to" corresponds to "verb inflection"?
Now, this particular book dates back to 1991, and I wonder if its assumption/view still holds today, or if it has been modified/discarded.
Thanks in advance.