Responsibilities and Obligations
Must and Have to
Must - Strong Personal Obligation
Use 'must' in the positive form to speak about strong personal obligations that you feel are crucial at the moment of speaking.
I must have my brain hard wired to the master controller.
I must send a high resolution jpeg to the publisher.
Have to - Responsibilities
'Have to' is used to indicate responsibilities at work. Use 'have to' to talk about daily responsibilities and obligation in general. 'Have to' is often confused with 'must'. The main difference is that 'have to' expresses obligation to work, family, friends, etc. 'Must' is used to indicate strong personal obligation that is felt at the moment of speaking.
'Have to' differs from other modal forms. 'Have to' is conjugated and followed by the base form.
Positive Form:
The company has to set up a sandbox and increase security.
Negative Form:
Peter doesn't have to worry about website hits.
Question Form:
Do they have to find a wi fi hot spot when they're supposed to be camping?
Had to
When speaking in the past, there is only one way to express obligation: 'Had to' We use 'had to' when we speak about past responsibilities and strong personal obligations.
Example:
Bob had to use an outdated scanner to digitize photos for the weekly periodical.
The epileptic employee had to avert her eyes when testing the new screensavers last week.
Must vs. Have To
'Have to' expresses everyday responsibilities at work, or for family and friends. 'Must' is only used for strong personal obligations.
Example 'Have to' for Responsibilities:
The company has to set up a sandbox and increase security.
Mary has to find a hired gun for every outsourced design project.
Example 'Must' for Strong Obligations:
I must have my brain hard wired to the master controller.
I must send a high resolution jpeg to the publisher.
The difference between 'have to' and 'must' in the negative is extreme. 'Not have to' signifies a lack of obligation. 'Mustn't', on the other hand, signifies prohibition. The past form of both 'must' and 'have to' is 'had to'
Example 'Have to' for No Obligation:
Peter doesn't have to worry about website hits.
The coder doesn't have to worry about making the program scalable.
Example 'Mustn't' for Prohibition:
One mustn't change your RSS feed too often.
Dana mustn't forget to purchase the hardware.