Descartes never used the word “function”. But it was he who made the idea possible: in Geometry, a curve stops being just a drawing and becomes a relationship between two numbers, $x$ and $y$. When one changes, the other changes along with it, following a rule. In this part, we tell you how this idea gained name, symbol and graphic.

The following five topics develop this reading and the subsequent history of the idea of ​​function.

All topics by René Descartes · ← Why does the rainbow appear at 42° · A ​​reading of the Cogito: listening and speaking →

Credits and sources of images.