How do you acquire and master adpositions in a L2? Please do not answer that only further exposure, practice or time are needed; they do not aid advanced L2 learners.
A native Anglophone, one family friend:
- majored in linguistics as an undergraduate;
- has been studying French as a L2, for over 50 years since kindergarten;
- has been living in France and communicates in French daily, for over 40 years;
- and so is now almost fluent in French.
Though he uses all Lexical and other Functional Morphemes perfectly, he still errs with adpositions. For example, he continues to confuse à with de with en with sur, or forgets which should be used. So he is interested in this question.