MODALS FOR NECESSITY (HAVE TO)

Hello everyone. 

As you know, this week we are looking at modal verbs to express necessity. Yesterday we looked at Must, a modal verb that adds Obligation to the main verb, and today we are going to look at a synonym of Must: HAVE TO

Example 1 (statement with no obligation):
I go to work every morning.

Example 2:
I have to go to work every morning. (I'm obligated by my boss, society, etc.)

Example 3:
I must call Anne. (Because it has been a long time since I've talked to her and I would really like to know how she is.)

Some textbooks mark a distinction between must and have to. They say that have to indicates external obligation and must indicates internal obligation (from yourself).
In reality, however, native speakers don't always follow this tendency and I therefore usually tell students not to worry about this difference.

There are a couple of other things to remember:
1) Like I said yesterday, the negative of must is must not or mustn't. However, the negative of have to is don't have to. You cannot say **haven't to**. 

2) The past of have to is had to, or didn't have to in the negative. There is no equivalent past for must, so it's past is also had to, or didn't have to in the negative.

Example 4 (present):
I must call Anne.

Example 5 (past):
I had to call Anne.

There is one last VERY important point. The negative of have to (don't have to) indicates lack of obligation, NOT negative obligation.

Example 6:
I don't have to call Anne.

This means that I don't have the obligation to call Anne. I can if I want to, but I'm not obligated to.

The negative of must (mustn't) indicates negative obligation.

Example 7:
I mustn't call Anne.

Example 7 means I have the obligation NOT to call her. In 6 I had a choice, in 7 I am being obligated not to do something.

If you have any questions about must and have to, please post them on one of our social media sites (Facebook or Twitter) and we will answer your questions as soon as possible. 

Have a great day!