Modal Verbs - an Introductory Lesson (B1, B2)

It's an introduction to modal verbs - first some basic rules, then the rules for forming past (not all modal verbs have separate forms for past, some use perfect infinitive - in my experience it is difficult for students to distinguish between the two, so I've thought of a rule to help them with that). Last but not least, a comparison between different meanings of the same modal verb (and their past forms).