"The Principles of Psychology, Volume 1 (of 2)" by William James is a textbook published in 1890. This groundbreaking work explores four key concepts: stream of consciousness, emotion, habit, and will. James examines brain function, sensory perception, and illusions while challenging previous notions of human thought. He introduces the revolutionary James-Lange theory of emotion and explores how instinct and experience shape behavior. This influential volume helped establish psychology's credibility as a science in America, impacting not only psychology but also philosophy and phenomenology for generations to come.