Grammar B2 - Mustn't and Don't Have to

The video explains how to express rules, duties, and permission in English through the following key concepts:

• Internal vs. External Obligation: When expressing current necessity, "must" generally refers to an internal obligation, while "have to" typically refers to an external rule or requirement imposed by others.
• Negative Forms:
  • "Mustn't" indicates that an action is strictly forbidden, such as following safety rules.
  • "Don't have to" indicates that there is no obligation, providing the individual with a choice.
• Past Obligations: "Must" lacks a past tense form, so "had to" is used as the universal phrase to describe any past obligation, regardless of whether it was internal or external.
• Permission:
  • "Can" is used for casual, present-tense permission.
  • "Be allowed to" is used to discuss the past or to emphasize that specific permission was explicitly granted by someone in authority.