How did Antoine Lavoisier define a chemical element?

Antoine-Laurent Lavoisier defined a chemical element using a simple operational approach: he classified an element as any substance that could not be further reduced or broken down into simpler components through any known chemical reaction.1

Building upon the earlier work of Robert Boyle, Lavoisier established this definition through meticulous, quantitative experimentation. By tracking the weights of all substances entering and emerging from reactions with high precision, he was able to identify substances that resisted decomposition. In 1789, he published a list of these elemental substances in his textbook, Traité élémentaire de chimie.21

While his methodology was revolutionary, his list still reflected some historical influence; he included substances like light and heat (caloric) as elements, as well as certain stable compounds—such as lime, alumina, and silica—that he could not decompose with the experimental tools available at the time.2