Must and Need

The speaker uses must to express what he has to do although this is often confused with have to or should. When it comes to the non-standard or watered down form of the language around the world, must is often used interchangeably with the other forms but then the distinction between how they are different is lost and the person might have to explain himself over again for the lack of being explicit.

Must is an obligation that is felt form the person who is expressing it whereas have to is applied externally. In another grammar book, I found no mention of this distinction but only a mention that must is used to tell people what to do. So I would think the standard form incorporates the distinction and the non-standard form does not. Must is also used interchangeably with need as both are used to express the importance of doing something that has to be accomplished.

Similarly mustn’t is used to advise people what they are not supposed to do. Both the affirmative and negative form of must are used to talk about a present or future action. The present form of must can be illustrated ina simples sentence like “I must go”. The future with must can be expressed by using elements of time like “tomorrow”, or “next week” but this is not to be confused with the use of the future tense. So if I say “I must see her tomorrow” the sentence is in the present tense but it has a future “sense”.