Or I should say in this forum: From whom one bounces ideas. Weaker than a co-author or collaborator. Not a confidant (no element of privacy or secrecy). Friend is too broad. Suggestions?
4 Answers
I would say sounding board.
Source: https://www.merriam-webster.com/dictionary/sounding%20board
In an artistic context, muse might fit the bill:
Source: http://www.oed.com/view/Entry/124057 (2.c.)
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Maybe, although to me, an artist’s “muse” is a woman who inspires someone else with her beauty. The mythical Muses supposedly gave Homer and Hesiod their ideas. Neither meaning would convey to me someone whose role is to listen to someone else’s ideas and give feedback.– DavislorSep 22, 2021 at 21:29
I would say a "Foil". Usually used to refer to characters in a story that compliment a more main character but I believe it works here too. I also think "foiling" or being a good foil for ideas is a practical and useful skill for an "Ideonomist", or someone who studies Ideas.
Although I would probably call this person a “sounding-board” as well, or say I “bounced ideas off” someone, writers sometimes call them a “beta reader.”