Hi all.

This question concerns writing fiction. How informal do you go with your writing?

Examples:
It is I who am sorry. (correct)
It is I who is sorry. (incorrect)

It is you who are mistaken. (correct)
It is you who's mistaken. (incorrect)

In both these cases I feel compelled to use the incorrect version. It's more informal, which I strive for in my writing (depending on the characters). Some would say I'm "writing down", and if taken too far, I'm certain that's true. But I think one of a writer's main responsibilities is getting out of the way of the story -- making the story as easy to read as possible and limiting your readers' stumbles. If I were reading the two correct examples above I would stumble. Yes, I know it might be possible to reword the examples, and if it's dialogue you write it the way the character would, but I'm referring to an interior monologue, and this is a question about formal versus informal

The problem is compounded further with my current work; one of the characters is a former English teacher.

Curious as to what others think. Thanks in advance!!