This unique intellectual portrait explores the role of ideas in Lincoln's life. Guelzo presents Lincoln as a serious thinker deeply involved in the problems of 19th-century thought, including those of classical liberalism, the Lockean Enlightenment, Victorian unbelief, and Calvinist spirituality. Lincoln emerges as a philosophical man who appropriates certain religious values without adhering to any religion, who insists on the pre-eminence of self-interest in spite of becoming the Great Emancipator, and who appeals to natural law and natural theology in politics while remaining a classical 19th-century liberal in principle. Based on primary materials from a wide variety of archives, this insightful work sheds light on the intellectual conflicts that led to civil war and that still influence today's "culture wars."