Our ancestors in ancient Greece and Rome used names to personify the forces of the heart. Startled by the beauty of a poem or melody, they judged a muse had assisted the artist. An exceptionally gifted person was thought to be possessed by a genie; such a person was named a genius.

But malevolent forces, too, invade the heart. When people became furious, our ancestors believed, an enraging spirit — a fury — had invaded them. The Christian Bible recounts stories of demoniacs — persons possessed by some destructive power.

James D. Whitehead, Evelyn E. Whitehead, Shadows of the Heart