Where did the idea of a thinking cap first come from? Someone had to start that idea.
As it turns out the origin of thinking cap was actually considering cap and that has been lost.
Lost, because people don’t use it and lost because it’s own origins are too far back to be remembered. Considering cap does seem older, which I like. It also describes the idea better. Considering things, rather than just thinking in general.
A ‘thinking cap’ was previously known by the appealing name a ‘considering cap’. That term has gone entirely out of use now but was known since at least the early 17th century, as in this example from Robert Armin in Foole upon foole, 1605:
“The Cobler puts off his considering cap, why sir, sayes he, I sent them home but now.”
via – The Phrase Finder
So, what does a considering cap look like? Is it decorative or plain? What gadgets and gizmos are on it? Does smoke come out of it if/ when it gets going or has been used too long? Is it heavy, shiny, red…?