Modals in the past form

Examples	Form	Time Reference
He can answer your question. They should leave early tomorrow. He had to leave at 7 this morning.	MODAL Simple Verb	Present Future Past
He might be joking!	Modal Continuous Form	Present
She can't have been serious! They might have gone to the country.	Modal Verbs Present Perfect	Past
They might have been working at that time	Modal Present Perfect Continuous Verb	Past