'fail to do' is (trying but) not succeeding (Halliday & Matthiessen 2014: 572)
whereas
'forget to do' is not doing according to intention (Halliday & Matthiessen 2014: 574).
Matters Arising Within Systemic Functional Linguistic Theory And Its Community Of Users
'fail to do' is (trying but) not succeeding (Halliday & Matthiessen 2014: 572)
whereas
'forget to do' is not doing according to intention (Halliday & Matthiessen 2014: 574).
But the Postmodifier does not itself enter into the logical structure, because it is not construed as a word complex.