Sep. 10th, 2010

From The Associated Press Stylebook, 2007:

engine, motor An engine develops its own power, usually through internal combustion or the pressure of air, steam or water passing over vanes attached to a wheel: an airplane engine, an automobile engine, a jet engine, a missile engine, a steam engine, a turbine engine.

A motor receives power from an outside source: an electric motor, a hydraulic motor.

It's so nice to have this cleared up. If it develops its own power, it's an engine. Otherwise, it's a motor. So your car has an engine, not a motor, unless it's an electric car, in which case it does have a motor. If it's a hybrid, it has one of each.

But what does "develops its own power" mean? An internal-combustion engine doesn't really develop its own power; it relies on fuel pumped in from outside. The same applies to anything—to get energy out, you have to put energy in. The only things that develop their own energy, with no outside help, are stars and small children.

From AP's discussion, it appears that taking in fuel, burning it, and using the resulting heat to create motion counts as developing your own power. And, somehow, so does receiving pressurized air, steam or water, but only if you pass it over "vanes attached to a wheel"—what we commonly call a turbine. Passing it through cylinders with reciprocating pistons doesn't count. So the "steam engines" used to propel locomotives and ships should be called steam motors.

And a rocket engine certainly develops its own power, in the simplest case of using internal combustion to move something—but it's apt to be called a "rocket motor," especially by rocket scientists. Someone should give those guys a clue.

As for an electric motor, it is forever denied the appellation "engine," though it seems to develop its own power quite as much as a steam turbine does. There's no big difference between using steam to turn a turbine and using electromagnetism to turn a rotor.

So AP's logic is looking shaky. Does etymology support it? No. "Engine" comes from the same root as "ingenious" -- the Latin ingenium, "inborn qualities, talent." "Motor," of course, comes directly from the Latin motor, "mover." Nothing about developing energy from within, or "vanes attached to a wheel." (Maybe AP uses this circumlocution to avoid the word "turbine" as prehistoric Northern Europeans used "brown one" to avoid their word for "bear.")

AP's distinction is simply a tangle of special pleading and whim, imposed on the language and the credulous by generations of petty self-appointed grammarians. The device that moves your car, no matter how it works, can properly be called a motor—it's a mover, isn't it? If we want to highlight its complex and ingenious design, we can call it an engine.

It's true that in common parlance electric "motors" greatly outnumber electric "engines." But that's a habit of speech; trying to prop it up with logic created after the fact just makes you look silly, as AP has demonstrated.

But General Motors and every state's Department of Motor Vehicles can heave a sigh of relief. They don't have to change their names.


Gan Ainm

September 2010

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