Boyle defines elements Robert Boyle (1627–1691) redefined an element to be a substance that could not be broken down into simple substances and questioned the elemental nature of Aristotle’s foursome. Boyle still believed transmutation (the conversion of "base" metals, such as tin or lead, into precious "noble" metals, such as silver or gold) was possible, however, and practiced alchemy. He also carried out important investigations of the behavior of gases, discovering the inverse relationship between the pressure and volume of a gas, known today as Boyle’s law.