Plato. Aquinas. Descartes. Kant. Freud. These great thinkers are still impacting the culture today—from public-policy decisions to world events, theology, the arts, education, and even everyday conversations. In this classic book, the late R. C. Sproul expertly surveys history's most influential streams of thought, proving that ideas are not just passing fads—they have consequences for generations to come. Helping readers better understand how many of these ideas have shaped their own thinking, this book will empower Christians to be a Christlike influence in the world.