We use modal verbs to talk about how certain something is. For present tenses, the modals go from less probable to more certain like this:
| Positive | Negative | Example | |
|---|---|---|---|
Less certain  More certain |
could might |
might not | Keenan might drive to school tomorrow, or he might not. He could be getting a ride from his brother. |
| may | may not | Keenan may not be driving to school tomorrow. Sometimes his sister needs the car on Tuesdays. | |
| should | shouldn't | Keenan should be driving to school tomorrow. He usually gets to use the car on Thursdays. | |
| must have to have got to |
must not can't couldn't |
Keenan has to be the driver. No one else on the team is old enough. Keenan couldn't be the driver. He hasn't passed his test yet. |
For future tenses, modals work very similarly, but there are a few differences on the more certain end of the chart.
| Positive | Negative | Example | |
|---|---|---|---|
| Less certain More certain |
could might |
might not | The tornado might hit us this week, but it could miss us completely if it keeps going along its current path. |
| may | may not | The tornado may hit us soon. We should be prepared in case it causes a lot of damage. | |
| should | shouldn't | The tornado shouldn't hit us. The weather report said it was going in the opposite direction. | |
| will | won't | The tornado won't hit us. It is on the other side of the country. |
For past tenses, modals are used to talk about different likelihoods for things that happened in the past.
| Positive | Negative | Example | |
|---|---|---|---|
| Less certain More certain |
could have might have |
might not have | My dog might have eaten some chocolate. He looks pretty ill. |
| may have | may not have | My dog may have eaten a piece of chocolate. I think there's one missing from this box! | |
| should have | shouldn't have | My dog shouldn't have eaten any chocolate. I think he knows he has to go to the vet if he does. | |
| must have had to have |
must not have can't have couldn't have |
My dog must have eaten some chocolate. He's throwing up all over the place and half my cake is missing! My dog couldn't have eaten chocolate. There's none in my house! It must have been something else. |
Exercise
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