Rationalism
The 17th-century school holding that reason, not sense experience, is the primary source of knowledge. Innate ideas exist. Descartes, Spinoza, and Leibniz built grand metaphysical systems from pure thought.
Sub-topics
Rene Descartes (1596-1650). Father of modern philosophy. Methodical doubt stripped away all beliefs until 'Cogito ergo sum' — I think, therefore I am. Mind-body dualism. Analytic geometry.
Baruch Spinoza (1632-1677). God and Nature are one substance (Deus sive Natura). Everything follows necessarily from God's nature. Ethics demonstrated in geometric order. Radical monism, determinism, and intellectual love of God.
Gottfried Wilhelm Leibniz (1646-1716). Reality consists of monads — indivisible, windowless units of perception. This is the best of all possible worlds (theodicy). Co-invented calculus. Universal logical language.