We use modal verbs to talk about how certain something is. For present tenses, the modals go from less certain to more certain like this:
| Positive | Negative | Example | |
|---|---|---|---|
|
Less certain
More certain |
could, might | might not | Jenny could be at home, or she might not be at home. |
| may | may not | Jenny may not be at home because she sometimes has basketball practice. | |
| should | shouldn't | Jenny should be at home. I saw her go home an hour ago. | |
|
must have to have got to |
must not can't couldn't |
Jenny must be home. I can hear her talking. Jenny couldn't be at home. I saw her go out a few minutes ago. |
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 package might arrive this week, or it could take until next month. |
| may | may not | The package may not get here in time for her birthday. | |
| should | shouldn't | The package should arrive by next Tuesday. | |
| will | won't | The package will arrive tomorrow. |
Modals are very important because they completely change the meaning of sentences. So choose your modals carefully.

I could eat the chocolate.

I shouldn't eat the chocolate.

I might eat the chocolate...

I will eat the chocolate!
Exercise
Open the exercise to begin the activity. Follow the instructions in the document.