Language: Necessary and Sufficient

Motivation

This is a nice piece of language I learned in school long, long ago.  It's very useful when talking about requirements or specifications for a project, acceptance criteria for a user story, etc.  Bonus: it makes you sound smart.

Example

The long and short of it is that what you want in order to work efficiently and effectively is the necessary and sufficient information (or tools or whatever).  Since I like working on cars, I'll use the simple example of changing a tire.

If you have the following, you have the necessary and sufficient toolset:

• a new tire
• a lug wrench
• a car jack

If you have the following, you have tools that are necessary, but not sufficient:

• a new tire

If you have the following, you have tools that are sufficient, but not necessary:

• a new tire
• a lug wrench
• a car jack
• a hammer

If you have the following, you have tools that are not necessary, and not sufficient:

• a hammer

Recap

Necessary defines the lower bounds of what you need while sufficient defines the upper bounds.  If you have both, you have the ability to do the work completely while being perfectly efficient.