Evaluates the conceptual novelty and disciplinary trajectory of 18th-century thought, emphasizing the pervasiveness of reason. In contrast to the Renaissance concern for maths-based systems, the Enlightenment sought for approaches to accommodate continuous, scientific progress. Descartes and Newton exemplified the former, while the French philosophes represented the latter, as they were responsible for introducing systemic analysis to philosophic thinking. Leibniz bridges this gap, due to his theory of entities (monads) in an ever-becoming status. Lessing, the poet, emerges the author’s final hero for adding to rationalism’s perfunctory analysis an endemic creative power. Deeply exploring concepts across many fields — science, religion, statecraft, psychology, aesthetics — this is a first-rate history of ideas.