Why Variables Changed Math

Before algebra, mathematicians solved each problem individually using words and geometry. The introduction of symbolic notation — using letters for quantities — let them state general rules once and apply them everywhere. Descartes standardized using x, y, z for unknowns in his 1637 treatise.

Today, every spreadsheet cell reference is a variable. Every programming loop counter is a variable. Every physics formula uses variables. The simple act of letting a letter stand for a number is one of the most powerful abstractions in human intellectual history.