In English there are various ways to describe rules and obligations. Here is a description of how to express obligation and how and when to use modal verbs.
The Difference Between Must, Have to, Shall, Need and May
PDF) A Logical Approach to Modal Verbs 3. “Must”
Che differenza passa tra necessaria e sufficiente? - Quora
The Difference Between Must, Have to, Shall, Need and May
The Difference between Since and For - Wall Street English
Must have - Free commerce and shopping icons, must have
The Difference Between Must, Have to, Shall, Need and May
How to Use Must, Have to, and Need to in English, must have
Must have - Free commerce and shopping icons, must have
Must have - Free commerce and shopping icons, must have
Qual è la differenza tra have to e has to? - Quora
