Fire

Fire is a thing. Most people think it's hot. It is made by an aggregate accumulation of phlogiston into a specific area.

Please keep in mind that were it not for fire, we would not have fire today.

For most purposes, fire can be reproduced with modern means by pressurized phlogiston container, called a "lighter" in mainstream Americana, and it can be used in a number of useful uses. For instance, you can burn down a forest with fire. So, if you pick one simple day when a forest just happens to get in your way, you can always pull out your handy modern "lighter" and burn it down. (That'll teach 'em!) You could always light other people on fire, but since many of them are not legimitate phlogiston attractors, they will not always stay on fire, which is presumed the preferred state.

If, for some strange reason, phlogiston theory is wrong, then fire does not exist.