Apart from their normal function as verbs, modals also appear in a number of other expressions.
The modal verb must, for example, can function as a prefix in adjectival phrases formed by adding must to verbs. The most common of these are must-see, as in 'Avatar is this month's must-see film’, must-read, as in ‘Click here to see a list of must-read questions on the environment’ and must-visit, as in ‘The south of the county is a must-visit destination for nature lovers’.
The noun a must also exists, meaning something you should have or do in a particular situation, as in ‘A good pair of binoculars is a must for any serious bird-watcher’ and ‘If you’re visiting New York, a trip on the Staten Island ferry is a must’.
Would is used in the expression would-be, meaning ‘aspiring or hoping to do or be something’, as in ‘The would-be thieves smashed a glass panel in the front door but fled empty-handed’, and ‘Hundreds of would-be actors queued for hours to be extras in the film’.
Can features in the adjectival expression can-do, meaning ‘keen to do different jobs and confident of success’, as in ‘You need to have a creative passion, a can-do attitude and a desire to work in a professional media environment’. If, on the other hand, you do not possess a can-do attitude, you might respond to requests to do things by using the informal expression ‘No can do', as in ‘No can do, I’m afraid. I need the boss’s signature for that’.