By Verbs, helping verbs

Milky wrote: [Check out this link "has to" as a helping verb? on the Linguistics forum. but it seems you haven't come to an agreement. and by the way I notice that I have made a mistake above. it should be like: "has to" is used to express internal obligations, and "must" for external...

Diamondrg wrote:but jim, where does the difference between "must" and "have to" lie then? as far as I know "must" expresses an internal obligation and "have to" an external one. Here, can "meeting the boss at the station" be an internal obligation. Not likely, I think. Why do you (native...