grammar - "I have to" vs. "I must"

When would you use the following?

• I have to go the market.


• I must go to the market.


• I need to go to the market.

If I replace 'have' with 'had' would you have any other way to say it? E.g. I had to go the market.

Answer

Have to contrasts with must in that it usually expresses an obligation imposed by someone other than the speaker. Had to is the past tense of have to and may be used in cases where a past equivalent of must is required. Need to is used where there is not such a strong obligation, but where completing the action will satisfy a particular requirement.