Dewey held that nature has different “transactions,” or kinds of action, that have mutual causes and effects between or among their components. Dewey’s transactions are thus interactions. There are three evolutionary levels, or “plateaus,” of transactions: physiochemical, psychophysical, and human experience. Physiochemical reactions are simply what can be studied by physics and chemistry; psychophysical transactions are connections between mind and body; human experience is exactly how things seem to human beings as they go about their lives.