Rationalism

Etymology

From Latin "ratio," "reason, calculation." As a school it is associated with the continental rationalists of the 1600s — René Descartes, Baruch Spinoza, and Gottfried Leibniz. Descartes set the template by doubting everything he could, until he reached one thing reason alone secured: “I think, therefore I am.”

noun · /RASH-uh-nuh-liz-um/
The view that reason, rather than sensory experience, is the primary source of genuine knowledge about the world.
What it names
A handle for the conviction that some truths are grasped by thinking them through — that the mind can reach certainties the senses could never guarantee.
Example
Her rationalism showed in how she trusted a clean logical proof over a messy pile of anecdotes.
Related idea
Empiricism is the counterweight, insisting knowledge must come through the senses. The two frame a centuries-long debate over where certainty actually comes from.