Rationalism is an epistemological view that regards reason as the primary source and test of knowledge. It contrasts with other potential sources like faith, tradition, or sensory experience, ie, empiricism.
Rationalists assert that certain principles in logic, mathematics, ethics, and metaphysics are so fundamental that denying them leads to contradiction. They have such confidence in reason that empirical proof and physical evidence are considered unnecessary for ascertaining certain truths.
This philosophical approach stands in opposition to empiricism. While rationalists emphasize innate knowledge and the intellect's ability to grasp logical truths directly, empiricists stress that knowledge is best gained through careful observation of the physical world via sensory experiences.
Rationalism has faced criticism for being disconnected from reality, as it assumes decision-making is a conscious, reflective process based on thoughts and beliefs. However, neuroscience research suggests that much of the brain's activity occurs at an unconscious level.