The speaker's attitudes and intentions
Can, may, must and want to
Obligation
Does someone need to do it?
modal verb
משמעות
Obligation shows that an action is required or necessary. Advice is weaker: it says what would be best, rather than what is required. Languages use special verb forms or separate words and phrases, and some have no special obligation form. Permission concerns what someone is allowed to do, not what they need to do.
איך לזהות
Look for what makes an action necessary or expected, and check whether the speaker presents it as a firm requirement or weaker advice.