247. The verb "devi" (cf. "devo", duty) is equivalent to the verb "must"
(which in English has no future, past, infinitive, etc.), and to "to
have to", "to be obliged to", etc., carrying the idea of "must" into all
tenses and moods. In the conditional mood its meaning is softened into a
vaguer sense (of "moral" obligation), and carries the idea of "ought":
Objektoj en la aero devas fali, objects in the air have to fall.
Ni devis agi laux la legxoj, we had to act according to the laws.
Vi devos iri, you must (will have to) go.
Sxi ne volas devi fari tion, she does not wish to have to do that.
Ili devigis min iri, they compelled me to go.
Vi devus iri, you should go (you ought to go).
Oni devus pensi antaux ol paroli, one ought to think before speaking.
Li estus devinta veni, he ought to have come.
Tio devus esti farita, that ought to have been done.