The author discusses the similarities between the concepts of the "imponderables"—a group of weightless substances including heat, electricity, and love—of the 19th century—and the psychodynamic factors of the 20th century. He espouses a new concept of affect in which it is viewed not as a substance or as inner states of one person but as part of a process in which the tensions and emotions of the family and other natural groups are determined by the configuration and motion of their systems.Abstract Teaser