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.)