Most Of The Machines We encounter in everyday life are one-way devices. Kitchen appliances turn bread into toast and cabbage into cole slaw, but they cannot perform the opposite transformations. Even machines that claim to be reversible adopt a very shallow notion of what it means to go backwards. The drill in my tool box has settings marked "forward" and "reverse," but no matter which I choose, I cannot undrill a hole. The gearshift in my car also has a position labeled R, but when I back up, the engine keeps turning in the same direction; if the car were truly reversed, it would suck in pollution through the tailpipe, converting it into gasoline and air.
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