Descriptions of modal verbs in learner grammars often evoke quite abstract semantic categories (focusing on dynamic, deontic and epistemic modality) in generalized usage contexts. Yet, in concrete utterances, modal verbs not only serve highly specific pragmatic and discourse-structural functions, but can also be shown to occur in (quasi-)formulaic sequences with specific lexical elements. These more idiosyncratic functional and formal properties are often insufficiently addressed in learner grammars. The article demonstrates, on the basis of two case studies, how insights and methods from Construction Grammar can help to improve the presentation of this topic. More specifically, it elaborates on the key determinants of L2 construction learning (involving frequency, proto-typicality and form-function mapping, among others) and illustrates what statistical techniques such as collostructional analysis and conditional inference trees can reveal about the intricacies involved in learning modal verb constructions.