Modal Verbs Necessity Or Obligation

Modal Chart

Necessity or Obligation

Sample sentences from the article:
Each of us has to finish two thick books….
…he was expected to complete…
Have to / Has to / Had to
Be expected to

These words express necessity or obligation. They usually indicate that someone else has imposed conditions on us. For example:

I have to take out the garbage. (It’s something I must do now. My mother told me to do it.)
I am expected to take out the garbage. (It’s a regular responsibility, a daily chore that my parents have given me.)

A related expression is be supposed to.

I am supposed to clean my room. (I’m required to do it.)

In the negative, these expressions have different meanings. For example:
I don’t have to go to the dance this weekend. (There is no obligation. I can choose to go or not.)
I’m not expected to go to the dance this weekend. (There is no expectation. People will be surprised if I do go.)
I’m not supposed to go to the dance this weekend. (I’m prohibited from going. It would probably be rude for me to go.)

Modals Chart

Modal	Past Modal	Negative	Negative Past
Can	Could	Can't Cannot	Couldn't Could not
Could	Could have	Could not	Couldn't have Could not have
Will	Would	Won't Will not	Wouldn't Would not
Would	Would have	Wouldn't Would not	Wouldn't have Would not have
May	May have	May not	May not have
Might	Might have	Might not	Might not have
Should	Should have	Should not	Should not have
Must	Had to Must have	Must not Mustn't	Must not have
Ought to	Ought to have	Ought not to	Ought not to have
Have to Has to	Had to	Don't have to Doesn't have to	Didn't have to Did not have to
Have got to Has got to
Be going to Be supposed to	Was/were	Is/are/am/not going to Isn't/aren't/am not supposed to	Wasn't/weren't going to Wasn't/weren't supposed to
Be able to	Was/were able to	Isn't/aren't able to	Wasn't/weren't able to
Be to	Was/were to	Is/are/am/not to	Wasn't/weren't to
Need to Needs to	Needed to	Doesn't need to	Didn't need to Needn't
Had better		Had better not
Used to		Didn't use to
Be about to	Was/were about to	Is/are/am not about to	Wasn't/weren't about to
Would rather	Would rather have	Would rather not	Would rather not have