The irregular verb devoir is a “shoe verb” in the present tense:
Devoir may express the following:
Obligation
Devoir shows that the subject “must,” “has to,” or “is supposed to” do something.
- Il doit travailler. (He must work or He has to work or He is supposed to work.)
- Il devait travailler mais il était malade. (He had to work but he was sick or He was supposed to work but he was sick.)
When used in the conditional, devoir means “ought to” or “should (have).”
- Je devrais le faire. (I should do it or I ought to do it.)
- J'aurais dû le faire. (I should have done it or I ought to have done it.)
Probability or supposition
- Elle doit être contente. (She must be happy or She is probably happy.)
- Elle a dû pleurer. (She must have cried.)
Debt
Devoir means “to owe” when it is followed by a noun:
- Il me doit cent dollars. (He owes me $100.)