William James propounded his theories of pragmatism in this book. He emphasized "radical empiricism" and the concept that the meaning of any idea - philosophical, political, social, or otherwise - only has validity in terms of its experiential and practical consequences. He wished to test competing systems of thought in the "marketplace of actual experience" to determine whether adopting a particular philosophical theory or way of looking at the world makes an actual difference in individual conduct or in how people perceive and react to the varieties of experience.