# Here's Why We Say 'Pushing The Envelope'

Apparently, it's got nothing to do with mail.

“Push the envelope.”

It’s a common phrase meaning “to go beyond the usual or normal limits by doing something new, dangerous, etc.”

But why does “pushing the envelope” mean this? The answer lies not in mail but in aeronautics.

When tracing the phrase’s origin, etymologists typically credit Tom Wolfe’s 1979 book about the U.S. space program, The Right Stuff, with popularizing it. Describing the work of test pilots, Wolfe wrote:

“One of the phrases that kept running through the conversation was ‘pushing the outside of the envelope.’ The ‘envelope’ was a flight-test term referring to the limits of a particular aircraft’s performance, how tight a turn it could make at such-and-such a speed, and so on. ‘Pushing the outside,’ probing the outer limits, of the envelope seemed to be the great challenge and satisfaction of flight test.”

As Wolfe noted, aviators use the term “flight envelope” to refer to a plane’s capabilities for a safe flight  ― it’s calculated by examining conditions like speed, altitude, engine power and more. Within this “envelope,” it is theoretically safe to fly.

The term envelope reportedly appeared in aeronautical contexts as early as 1901 in reference to inflating balloons or airships. The “envelope” is the term for the bag of air in a balloon or airship.

The envelope is also a mathematical concept referring to a curve that is tangential to each member of a family of curves in a plane. The envelope has been defined as “the locus of the points of ultimate intersection of consecutive curves of a family.” A classic example is a ladder sliding down a wall; you can calculate the envelope of the various positions of the sliding ladder.

The verb “to envelop,” which has French origins, means to completely surround, wrap up or cover ― so it’s not surprising the related noun “envelope” came to refer to an enclosing bag or outer boundary.

The “flight envelope” concept Wolfe described dates back at least to World War II. A 1944 volume of the Journal of the Royal Aeronautical Society notes, “The best known of the envelope cases is the ‘flight envelope’, which is in general use in this country and in the United States ... The ‘flight envelope’ covers all probable conditions of symmetrical manoeuvring flight.”

The year before Wolfe’s book helped usher the “push the envelope” phrase into general usage, the expression appeared in a July 1978 issue of Aviation Week & Space Technology: “The aircraft’s altitude envelope must be expanded to permit a ferry flight across the nation. NASA pilots were to push the envelope to 10,000 feet.”

Again, to fly within the “envelope” formed by those limits is theoretically safest. Therefore, to “push the envelope” is to test those limits by taking an aircraft to or beyond those parameters.

These days, “pushing the envelope” appears in all sorts of contexts: fashion, sports, politics, comedy and more. But honestly, when you think about the potential danger of “pushing the envelope” in flight, it removes the element of daring and risk from all other examples.