Maria: I'm so excited! I'm going to Disneyland this weekend.
Neil: Have you been before?
Maria: No, I've never been.
Neil: You'll have a great time
Maria: Which rides should I go on? I like fast rides.
Neil: Then you should definitely go on Space Mountain. It's a must. And the railroad and Matterhorn are pretty fun as well.
Meaning: While "must" is normally used in English as modal, it can be used as a noun meaning something that is indispensable or required. However, while "must" usually has a formal meaning when used as a modal, it's often used as a noun in informal situations, when someone is giving a suggestion of something that is worth doing. In the example above, Neil says that the ride Space Mountain is a must, meaning that Maria should make sure to go on it. Usually, "must" is used as a noun in the phrase "to be a must."
Here is another example:
Having a car is a must if you hope to live and work in Los Angeles. While the public transportation is acceptable for visitors, it's usually not reliable enough for everyday commuting.
Meaning: In this case, it's being suggested that a car is necessary for those living and working in Los Angeles due to unreliable public transportation.
This idiom is from LSI's new edition of "Reading Horizons," which will be used in the Level 6 Reading classes. For more information, please visit http://www.languagesystems.com/