Rationalism asks where certain knowledge comes from. Its answer: from reason. The senses deceive, but the mind can reach necessary truths, like those of mathematics, by deduction from self-evident principles. Many rationalists also hold that we are born with certain ideas, such as those of number or of God. The ideal is to build knowledge like a geometric structure, step by step and without gaps.
It flourished in seventeenth-century Europe. Descartes sought an indubitable foundation and found it in 'I think, therefore I am'. Spinoza wrote his Ethics in geometric form, identifying God with nature. Leibniz held that nothing happens without a sufficient reason. Rationalism debated British empiricism, and Kant later tried to reconcile the two. In Brazil, Marilena Chauí has devoted decades to studying Spinoza, linking his philosophy to the defense of democracy.
Core ideas
Reason is the most secure source of knowledge
Some ideas are innate and do not come from experience
Everything has a reason that can be understood
Where to start reading
Each thinker's starter book, picked for beginners.
