The Life of Reason is a five-volume work by the Spanish-American philosopher George Santayana. Published between 1905 and 1906, it is considered one of the most important works of philosophy of the early 20th century. The book explores the nature of reason and its role in human life, from the development of common sense to the pursuit of knowledge and the creation of art. Santayana's philosophy is strongly influenced by the materialism of Democritus and the refined ethics of Aristotle, with a special emphasis on the natural development of ideal ends. The Life of Reason is known for its elegant prose and insightful observations on human nature.