Martha asks, "Where does the phrase 'By the Seat of your Pants' come from?"

Well, Martha, I didn't know the answer to this one, so I checked a few different sources, and was able to piece together what seems like a reasonable explanation.

The one thing that all the sources agree on is that it's an old aviation expression. That makes sense, because the full phrase is typically "flying by the seat of your pants," even when the expression is being used in other contexts. For example, if you're playing volleyball, and you don't know how to serve, you wouldn't (probably) say "serving by the seat of my pants" you would still say "flying by the seat of my pants" even though you're not actually flying.

So where does this expression come from? What does it mean to "fly by the seat of your pants?"

Well, in the early days of aviation, the instruments for determining how fast you're going, what angle you're flying at, etc, were not very sophisticated, and in some cases either weren't installed in a plane, or malfunctioned in mid-flight. If that happened, you had to, in an almost literal sense, fly by the seat of your pants.

How would you know if your plane was declined from horizontal? Your "seat" started sliding forward in the pilot's chair. If you felt like you were going to land butt first on the floor, that was a pretty good indicator that you were on a pretty steep descent. Similarly, if you felt like your backside was getting pushed backward, it's a good bet that you're ascending.

What about banking? Well, if you've studied circular motion (or if you've just sat in a car taking a corner quickly!) you know that when the chair you're sitting in takes a corner, your body has a tendency to keep going in a straight line, until you start pressing up against the door, or the side of the chair. So if the plane is banking, you'll feel it in the seat of your pants, because you'll start sliding sideways in the chair.

So pilots who were very experienced could successfully fly a non-instrumented plane based solely on how their derriere was situated in the pilot's chair!

Today, it has taken a more idiomatic meaning. It simply means to do something without planning or organizing, or improvise. To put it another way, it's the same as "winging it," which - interestingly - is not an aviation metaphor. It's a theatrical metaphor, meaning that the person was doing last minute practicing in the stage wings (the offstage area where people waited before performing).

Flying by the seat of your pants. Winging it. Both mean to improvise, but they have vastly different origins!