Here is a synopsis of past and present tenses of some modal verbs:
Use different modal verbs in your request depending on the level of politeness needed.
Family dinner: Could you pass the salt, please?
Dinner at a nice restaurant: Would you pass the salt, please?
Dinner at the palace with the King and Queen: Might you pass the salt, please?
There is a change in pronunciation when the verb “to have” is used as a modal auxiliary in the expression “to have to,” meaning “must.”
She has a dog. (HAZ) She has to be home by midnight. (HASS)
We have three cats. (HAV) We have to be home before dark. (HAFF)
I don’t know why. That’s just how it is.