The **exact sciences** or **quantitative sciences**, sometimes called the **exact mathematical sciences**,^{[1]} are those sciences "which admit of absolute precision in their results"; especially the mathematical sciences.^{[2]} Examples of the exact sciences are mathematics, optics, astronomy,^{[3]} and physics, which many philosophers from Descartes, Leibniz, and Kant to the logical positivists took as paradigms of rational and objective knowledge.^{[4]} These sciences have been practiced in many cultures from antiquity^{[5]}^{[6]} to modern times.^{[7]}^{[8]} Given their ties to mathematics, the exact sciences are characterized by accurate quantitative expression, precise predictions and/or rigorous methods of testing hypotheses involving quantifiable predictions and measurements.^{[9]}

The distinction between the quantitative exact sciences and those sciences that deal with the causes of things is due to Aristotle, who distinguished mathematics from natural philosophy^{[10]} and considered the exact sciences to be the "more natural of the branches of mathematics."^{[11]} Thomas Aquinas employed this distinction when he said that astronomy explains the spherical shape of the Earth^{[12]} by mathematical reasoning while physics explains it by material causes.^{[13]} This distinction was widely, but not universally, accepted until the scientific revolution of the 17th century.^{[14]} Edward Grant has proposed that a fundamental change leading to the new sciences was the unification of the exact sciences and physics by Kepler, Newton, and others, which resulted in a quantitative investigation of the physical causes of natural phenomena.^{[15]}

Linguistics and comparative philology have also been considered exact sciences, most notably by Benjamin Whorf.^{[16]}