Example of error:
(1) I don't think that a worker has to earn the same as a doctor.
Have (got) to is in many instances synonymous with must, expressing obligation or high probability, e.g:
You must/have (got) to be home by midnight.
Somebody must/has (got) to know the answer.
As pointed out above (2.6-3) must meaning 'obligation' is preferred when the will or authority of the speaker is involved (e.g. when giving an order); have (got) to is preferred when the obligation derives from some external authority or circumstance not identifiable with the speaker's will. Cutting across this constraint is the fact that Americans, at least, feel must to be more formal and prefer have (got) to in both instances in colloquial speech, A further difference between must and have (got) to in their 'probability' meating-is that have (got) to is more emphatic. In the (second) example above, this difference is not discernible, but in some contexts the emphatic'tone of have (got) to would be inappropriate, e.g.:
(The doorbell rings)
"That must be the plumber. We've been expecting him."
(Addressing a stranger)
"Oh hello! You must be the new typist.
In negative sentences, as mentioned above (2.6-3),, don't have to expresses lack of obligation or necessity, but this is not what was meant in (1). Here the speaker is expressing an opinion about the desirability of a hypothetical situation (whether or not a worker should earn as much as a doctor), which requires should.