The Age of Reason was a period of great intellectual activity that began in the 1600’s and lasted until the late 1700’s. The period is also called the Enlightenment. Philosophers of the Age of Reason stressed the use of reason, as opposed to the reliance on authority and scriptural revelation. For them, reason provided means of attaining the truth about the world and of ordering human society to assure human well-being. The leading philosophers included Descartes, Locke, Berkeley, and Hume. They also included Jean Jacques Rousseau, Voltaire, Denis Diderot, and other members of a group of French philosophers called the philosophes.
Locke’s philosophic ideas were characteristic of the Age of Reason. Locke sought to determine the limits of human understanding and to discover what can be known within those limits that will serve as a guide to life and conduct. He tried to show that people should live by the principles of toleration, liberty, and natural rights. His Two Treatises of Government (1690) provided the philosophic base for the Revolutionary War in America and the French Revolution in the late 1700’s.
The Philosophy of Immanuel Kant, a great German philosopher of the late 1700’s, became the foundation for nearly all later developments in philosophy. Kant’s philosophy is called critical philosophy or transcendental philosophy. Kant was stimulated by the skeptical philosophy of Hume to try to bring about a synthesis of rationalism and empiricism. In his Critique of Pure Reason (1781), Kant tried to provide a critical account of the powers and limits of human reason, to determine what is knowable and what is unknowable. Kant concluded that reason can provide knowledge only of things as they appear to us, never of things as they are in themselves. Kant believed that the mind plays an active role in knowing and is not a mere recorder of facts presented by the senses. The mind does this through basic categories or forms of understanding, which are independent of experience and without which our experience would not make sense. Through such categories and the operations of the mind, working on sense experience, we can have knowledge, but only of things that can be experienced.
Kant criticized the traditional arguments for the existence of God. He argued that they are all in error because they make claims that go beyond the possibility of experience and thus go beyond the powers of human reason. In his Critique of Practical Reason (1788), Kant argued that practical reason (reason applied to practice) can show us how we ought to act and also provides a practical reason for believing in God, though not a proof that God exists.