for fear thatIntroduces a feared possibility and is followed by the subjunctive. In formal French, ne may appear without expressing negation, as in « de peur qu'il ne pleuve »; the phrase can also be followed by « de » and an infinitive when the subject is the same.
FR: Elle a parlé doucement de peur que les enfants ne se réveillent.
EN: She spoke quietly for fear that the children might wake up.