This table shows us the past tense of ‘must’ and ‘have to’.
We also see how the past tense of ‘must’ depends on whether we are expressing obligation or our personal opinion about probability.
| Must / have to |
present |
past |
|
When expressing obligation: I must go. / I have to go. |
When expressing obligation, the past of 'must' and 'have to' is always 'had to': I had to go. They had to be there at 2 o'clock. |
|
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When expressing a personal opinion about probability (deduction), we use 'must' to express that we feel something is true: He must be here. It must be great. |
When expressing a personal opinion in the past, we use 'must have', not 'had to': He must have been here. It must have been great. |
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