Alchemy is an influential tradition whose practitioners have, from antiquity, claimed it to be the precursor to profound powers. The defining objectives of alchemy are varied but historically have typically included one or more of the following goals: the creation of the fabled philosopher's stone; the ability to transmute base metals into the noble metals (gold or silver); and development of an elixir of life, which would confer youth and longevity.Though alchemy played a significant role in the development of early modern science, it differs significantly from modern science in its inclusion of Hermetic principles and practices related to mythology, magic, religion, and spirituality. It is recognized[by whom?] as a protoscience that contributed to the development of modern chemistry and medicine. Alchemists developed a structure of basic laboratory techniques, theory, terminology, and experimental method, some of which are still in use today. However, alchemists predated modern foundations of chemistry, such as scientific skepticism, atomic theory, the modern understanding of a chemical element and a chemical substance, the periodic table and conservation of mass and stoichiometry. Instead, they believed in four elements and phlogiston, and cryptic symbolism and mysticism was an integral part of alchemical work.