Who authored a significant textbook in 1890 that contributed to the formation of psychology as a discipline?

The correct answer is William James, who authored "The Principles of Psychology" published in 1890. This textbook is considered one of the foundational texts in psychology, as it systematically explored various psychological concepts and experimented with the application of psychology to different aspects of human experience. William James's work helped lay the groundwork for establishing psychology as an academic discipline separate from philosophy and biology.

James introduced important ideas such as the stream of consciousness, the self, and the functional aspects of mental processes, which influenced many later psychologists. His emphasis on pragmatism and the exploration of psychological phenomena from a practical standpoint significantly shaped the trajectory of psychology, making his contributions key to the field's development during that era.