Well, my personal 'muse' and 'inner critic', I just realized, often take on the form of the protagonists of my books. My preferred style is first-person narrative, with two opposing viewpoints that alternate each chapter. The muse and inner critic are very opposing in what they want to do, so this is fitting.
Example: in Faerie Games, Melissa is my inner critic, Finn is my muse. Melissa is the nitpicky, organized one who always knows how to fix things, who likes a plan, an outline. Finn is the erratic, moody premadonna who strikes at the most inopportune time with spurts of genius and carefree creation. Polar opposites who argue constantly, yet when they work together, it's magic.
With the next pair of protagonists, I think the defining line is going to be a lot more erratic. I'm hoping to work on Fianna next, focusing on Helen (crazy, impulsive, controlling mother) and Lucy (creative, calm, worry wart daughter). Maybe I'll need to employ Yoel (negotiating, history loving, brainiac leader figure) to be the sole inner critic and oversee all of his crazy-muse women.
How about you guys? Do you have any characters that would fit these roles too perfectly or do your inner critic and muse have lives of their own?