Usage of "Must" in speaking

 The modal verb "must" is used in speaking to convey various meanings and functions:

Necessity or Obligation: "Must" is frequently used to express a strong necessity or obligation.

   - "I must finish this report by tomorrow morning."

   - "You must wear a seatbelt when driving."

Certainty or Strong Deduction: "Must" can indicate a high degree of certainty or strong deduction based on evidence or logical inference.

   - "She's been studying all night; she must be prepared for the exam."

   - "There's no response from their end; they must be out of the office."

Prohibition: In negative statements, "must" can convey a prohibition or a strong prohibition.

   - "You must not smoke in here; it's against the rules."

   - "You mustn't touch the paintings in the museum."

Advice or Recommendation: Sometimes "must" is used to give strong advice or recommendations.

   - "You must try the seafood pasta at that restaurant; it's amazing!"

   - "If you want to succeed, you must never give up."

Expressing Conviction or Resolution: "Must" can also convey a strong conviction or resolution.

   - "I must find a way to solve this problem."

   - "We must stand up for what is right."

Inferences or Conclusions: "Must" can be used to draw inferences or conclusions based on available information.

   - "With all the traffic, they must be running late."

   - "The phone is ringing; it must be John calling."

"Must" is a versatile modal verb that is used to express a sense of necessity, obligation, certainty, prohibition, advice, conviction, or inference in spoken English. Its usage can vary depending on the context and the speaker's intention.