Exploration Through Example

I used to play a game with my daughter when she was around eight. I’d ask her to define a peanut butter sandwich. She’d say something like “bread with peanut butter on it.” I’d say, “So if I take a slice of bread and put a jar of peanut butter on it, that’s a peanut butter sandwich?” She’d say, “No, it’s a piece of bread with peanut butter spread on it.” And I’d say, “So if I spread peanut butter on both sides of a piece of bread, that’s a peanut butter sandwich?”

This game can go on for a long time.

I was of course trying to teach her that there is no such thing as an unambiguous requirement. Ambiguity is a three-way relationship between a reader, her conception of the writer, and the text.

“Her conception of the writer”: to some people, a peanut butter sandwich has two slices of bread. The raw statement “get me a peanut butter sandwich” is ambiguous until you know which kind of person uttered the statement.

A lot of knowledge of the writer/utterer is not conscious, because conscious thought is inefficient. We spend a lot of time just knowing that other people know that we know what they want. When Sophie asks for a peanut butter sandwich, I short-circuit any consideration of what a peanut butter sandwich really is by knowing what she wants and knowing what past actions have caused her to be satisfied.

That’s part of the reason why requirements are most efficiently transmitted face-to-face.

UPDATE: Joseph Bergin contributes a requirement that depends critically on shared background knowledge and a willingness to overrule the literal meaning: