Fire is not a matter..Fire is a process involving both. Fire is the energetic combination of various substances with oxygen to release light and heat. In a gas fire, such as might be found on a stove or in a heater, a light hydrocarbon such propane is broken down into components of hydrogen and carbon which unite with oxygen from the atmosphere to form water and carbon dioxide. In an ordinary wood fire, heat causes the wood to break down and release hydrocarbons which then burn as propane would.