1.4 Substance

Main article: Chemical substance

Substance may refer to:
Chemical substance, in chemistry, any material with a definite chemical composition
Physical substance, any quantity of material with any density, which can be measured or perceived without changing its identity.
Substance theory, in philosophy, that which "stands under" or supports the existence of properties; a particular, concrete object; or what exists only by itself (causa sui)
Substantial (rapper)
Substance (Joy Division album)
Substance (New Order album)
"Substance", a song by Haste the Day from That They May Know You and Burning Bridges
Metal Gear Solid 2: Substance, a tactical espionage video game

A chemical substance is a kind of matter with a definite composition and set of properties. Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture; for example: air, alloys, biomass, etc.
Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming chemical compounds. Earlier in the history of chemistry substances were given name by their discoverer, which often led to some confusion and difficulty. However, today the IUPAC system of chemical nomenclature allows chemists to specify by name specific compounds amongst the vast variety of possible chemicals. The standard nomenclature of chemical substances is set by the International Union of Pure and Applied Chemistry (IUPAC). There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system. Inorganic compounds are named according to the inorganic nomenclature system.In addition the Chemical Abstracts Service has devised a method to index chemical substance. In this scheme each chemical substance is identifiable by a number known as CAS registry number.