When thinking about a situation, it often helps to look at two or three salient features and graph them. A person has an age, a weight, and a height; a car's engine has revolutions per minute and power output; a book has a price and a page count; a nation has a population, a gross domestic product, and a land area; an airplane wing has a speed and an angle of attack; and so forth. If we take a large sample of people and plot their ages, weights, and heights, we'll see that they tend to display patterns. Infants are usually light and short. Tall people at any age tend to weigh more.
The shape that this kind of graph assumes is called the envelope. Looking at it sometimes yields unexpected insight. Humans have great pattern-recognition abilities, and studying the envelope of a system can reveal subtle relationships, places where ordinary behavior breaks down. "Pushing the envelope" --- that is, exploring the edge of what is possible, and trying to go beyond it --- may also lead to new discoveries, as well as to better understanding of why things are the way they are.
Wednesday, August 25, 1999 at 21:36:16 (EDT) = Datetag19990825