1. Overview of “Must” and “Have To”

Both “must” and “have to” indicate that something is necessary or required. However, there are differences in how they are used and their nuances:

• “Must” often suggests a strong, personal obligation or rule, and it can be more formal.
• “Have to” tends to be used for general obligations, rules, or external requirements.

2. When and How to Use “Must”

“Must” is used to express strong necessity, duty, or a recommendation that comes from the speaker’s perspective. It’s often used for:

• Personal feelings of necessity or strong advice.
• Rules and instructions in formal contexts.

Examples:

• Personal Obligation:
  “I must finish this project by tonight.” (The speaker feels it’s crucial.)
• Strong Advice:
  “You must see this movie! It’s amazing!”
• Formal Instructions:
  “Guests must check out by 11 a.m.”

Tip: “Must” is generally only used in the present and future tense and doesn’t have a past tense form. To express past obligations, we use “had to.”

3. When and How to Use “Have To”

“Have to” conveys an obligation that usually comes from outside sources, such as rules, laws, or circumstances beyond the speaker’s control. It is more common in everyday speech.

Examples:

• External Obligation:
  “I have to wear a uniform at work.” (A rule or requirement at work.)
• General Rule or Fact:
  “We have to drive on the right side of the road here.”

Tip: Unlike “must,” “have to” can be used in all tenses (past, present, future). For example:

• Past: “I had to cancel the meeting yesterday.”
• Present: “I have to go now.”
• Future: “I will have to study more for the exam.”

4. Nuances and Key Differences

• Degree of Formality:
  “Must” tends to sound more formal and urgent, while “have to” feels more neutral and is more commonly used in daily conversation.
• Personal vs. External Obligation:
  “Must” is often for personal commitments or strong advice; “have to” points to rules or conditions imposed by someone else.

Examples for Comparison:

• “I must be home by 10.” (A personal rule or promise.)
• “I have to be home by 10.” (An external rule, such as a curfew set by parents.)

5. Negative Forms: “Mustn’t” vs. “Don’t Have To”

• “Mustn’t” expresses prohibition—something is not allowed.
  Example: “You mustn’t park here.” (It is not permitted.)
• “Don’t have to” indicates a lack of necessity—it’s optional.
  Example: “You don’t have to come if you’re busy.” (It’s not required.)

6. Practice Exercises

Fill in the blanks with the correct form of “must”, “mustn’t”, “have to”, or “don’t have to”:

1. You _______ speak loudly in the library.
2. I _______ call my friend to confirm the meeting.
3. She _______ leave early yesterday due to an emergency.
4. You _______ bring food; we already have plenty.

Answers:

1. mustn’t
2. have to
3. had to
4. don’t have to