Philosophical Rationalism is a theory that emphasizes reason as the primary source of knowledge. Rationalists believe that certain truths can be known through intellectual deduction rather than sensory experience. This approach often contrasts with empiricism, which prioritizes observation and experience in the acquisition of knowledge. Key figures in Rationalism include René Descartes, who famously stated, "I think, therefore I am," highlighting the importance of doubt and reasoning. Other notable rationalists, such as Baruch Spinoza and Gottfried Wilhelm Leibniz, contributed to the development of rationalist thought, advocating for the use of logic and mathematics to understand the world.