I kind of have an idea of when 了 and 过 should be used but it's mostly on a case by case basis, and I don't know the exact rules. So if I want to express something that happened in the past, when ...
In a sentence such as "因为我去面试了，所以我刮了胡子", in one case, 了 is after the sentence, while in the other case it's after the verb, even though in both cases, 了 is used to express the past tense. So how to ...
In this sentence: 他曾经在北京学过两年汉语。 what's the role of 曾经 ? I understand that 过 already implies that the action happened in the past.