For many years chemists have classified substances into acids or bases. Lavoisier thought that acidic substances owed their behavior to the presence of oxygen. But it was Humphry Davy in 1810 who showed that the element that all acids have in common is hydrogen.

The first acid-base theory was developed by Svante Arrhenius in 1884, explaining acidity as the ability of a substance to dissociate by giving up protons, and basicity as the ability to give up hydroxide ions.

In 1923, Bronsted and Lowry proposed a theory that the acid was a proton donor and the base was an acceptor, so that acid-base reactions occurred via conjugate acid-base pairs.