The modal verbs include can, must, may, might, will, would, should. They are used with other verbs to express ability, obligation, possibility, and so on. Below is a list showing the most useful modals and their most common meanings:
| Modal | Meaning | Example | 
| can | to express ability | I can speak a little Russian. | 
| can | to request permission | Can I open the window? | 
| may | to express possibility | I may be home late. | 
| may | to request permission | May I sit down, please? | 
| must | to express obligation | I must go now. | 
| must | to express strong belief | She must be over 90 years old. | 
| should | to give advice | You should stop smoking. | 
| would | to request or offer | Would you like a cup of tea? | 
| would | in if-sentences | If I were you, I would say sorry. | 
Modal verbs are unlike other verbs. They do not change their form (spelling) and they have no infinitive or participle (past/present). 
The modals must and can need substitute verbs to express obligation or ability in the different tenses. Here are some examples:
| Past simple | Sorry I'm late. I had to finish my math test. | 
| Present perfect | She's had to return to Korea at short notice. | 
| Future | You'll have to work hard if you want to pass the exams. | 
| Infinitive | I don't want to have to go. | 
| Past simple | I couldn't/wasn't able to walk until I was 3 years old. | 
| Present perfect | I haven't been able to solve this problem. Can you help? | 
| Future | I'm not sure if I will be able to come to your party. | 
| Infinitive | I would love to be able to play the piano. 
 
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Modals are 
auxiliary verbs. They do not need an additional auxiliary in negatives or questions. For example: 
Must I come? (
Do I must come?), or: 
He shouldn't smoke (
He doesn't should smoke).
A quiz on modals: