An Enquiry Concerning Human Understanding

PART I.

20. All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, _Relations of Ideas_, and _Matters of Fact_. Of the first kind are the sciences of Geometry, Algebra, and Arithmetic; and in short, every affirmation which is either intuitively or demonstratively certain. _That the square of the hypothenuse is equal to the square of the two sides...