Or when you know it must be there somewhere but you have no idea what it looks like?

Or when you have no idea how to formulate your query?

Or when you would like to expand your exploration to adjacent or not-so-adjacent concepts?

If your only guiding principle is the "obscenity principle"--I know it when I see it--you need not a search engine but a hunch engine.

A hunch engine uses interactive evolutionary algorithms to help users navigate large spaces, combining the ability of computers to sift through massive amounts of data and that unique human ability to see "stuff" (sometimes even when stuff is not there) with their right brains. The hunch engine enables a form of "high-throughput screening by humans."

Bonabeau presents applications that relate to consumer data mining, drug discovery, and web search.