What is the active principle of burning, characterized by the heat and light of combustion?

The active principle of burning, characterized by both heat and light, is understood as fire. Fire is the overall reaction that occurs during combustion, encompassing the heat, light, and chemical processes involving fuel and oxygen. It is the manifestation of energy released when a fuel undergoes rapid oxidation, producing heat and light.

Flame, while often associated with fire, refers specifically to the visible, gaseous part of fire that emits light and is a result of combustion. Smoke consists of various particulate matters and gases that are produced during combustion but do not encapsulate the essence of burning itself. Embers are the glowing remnants of a fire, primarily made up of hot ashes or coals, which emit heat but do not actively signify the combustion process as a whole. Therefore, fire, as the complete phenomenon of combustion, is the correct identification of the active principle of burning.