Subjunctive rule one
You can use French verbs in the subjunctive mood, which is used to express an attitude, an opinion, or personal will, or to imply hypothesis or doubt.
Subjunctive rule two
The subjunctive is used after many impersonal expressions that state an opinion.
Subjunctive rule three
When the main clause of a sentence expresses will or emotion, use the subjunctive in the subordinate clause.