In 16th century Europe, some specialists in natural sciences, physicians, Protestant theologians cast doubt on the existence and action in human affairs of angels, demons, and departed souls. A French erudite, Pierre Le Loyer, defends traditional catholic convictions about those Spirits in the last years of the century and then develops what he calls a Spectres' science. He tries so to register the examination of Spirits in human sciences, which progress independently of theology in the 17th century.