Can x Can´t

Can is a modal. And what´s a modal: it´s not a verb, but it modifies a verb.

1. Modal verbs do not take "-s" in the third person.
Examples:

• He can speak Chinese.

2. You use "not" to make modal verbs negative, even in Simple Present and Simple Past.

Examples:

• He should not be late.

3. Many modal verbs cannot be used in the past tenses or the future tenses.

Examples:

• He will can go with us. Not Correct

Can tells about a possibility or a permission. For example:

You can drive if you are over 18. ( Permission)
You can´t vote if you are under 16. (Permission)


You can get bloated if you eat a lot of cheese. (Possibility)