Past Modals

We do not form the past tense of modal verbs with –ed.

Many modal verbs do not have a past tense form. To form the past tense of modal verbs we either:

1. Change a word.

2. Use a modal verb + have + Past Participle

When we use this structure, these verbs have a special meaning.

Verb	Function	Example	Meaning
Should have	Regret	I should have gone to bed earlier.	I went to bed late and now I regret it.
Shouldn’t have	Regret	I shouldn’t have gone to bed so late.	I went to bed late and now I regret it.
Must have	Deduction	I can’t find my keys. I must have left them at home.	I’m 99.9% sure I left my keys at home.
Can’t have	Deduction	I can’t find my keys. I can’t have put them in my bag.	I’m 99.9% sure I didn’t put my keys in my bag.
May/Might/Could have	Supposition	I can’t find my keys. I may/might/could have left them at home.	It’s possible that I left my keys at home. I’m not sure.
May/might not have	Supposition	I can’t find my keys. I might not/may not have put them in my bag.	It’s possible that I didn’t put them in my bag. I’m not sure.
Could have	Ability not realised	He could have helped her.	He could have helped her but he didn’t.

Click on the links below to learn more about modal verbs