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KEY TAKEAWAYS
- The basic formula for using a modal auxiliary is
| subject | + | modal auxiliary | + | main verb | 
- There are ten main modal auxiliaries in English: can, could, may, might, shall, should, will, would, must, and ought to.
- The four common types of errors when using modals include the following: using an infinitive instead of a base verb after a modal, using a gerund instead of an infinitive or a base verb after a modal, using two modals in a row, and leaving out a modal.
- In the present perfect tense, when a sentence has a modal auxiliary before the verb, the helping verb is always have.
- The two common errors when using modals in the present perfect tense include using had instead of have and leaving out have.
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