One modern (I think) literary convention is that unless the story is written in first-person POV, internal dialogue is expressed in italics, so that the reader doesn’t mistake the character’s thoughts for things he or she says out loud. Not every writer does this, but it’s common.
In writing the Altered Seasons books, I’m experimenting with this a little. Isabel has a number of internal conversations with something that poses as her conscience but may actually be just a lump of internalized negativity with delusions of wokeness. I’m using bold rather than italics to distinguish this particular inner voice, as follows:
You calmly told Governor Camberg that Miami and New Orleans were lost causes. Now you’re shedding tears over a place whose whole population could fit into one housing project in either of those cities. Parochial much?
Smith Island is different. It literally has its own accent. Last time Mom and I got to talking about Sandy, Mom slipped and said “billionahrr.” If we lose it, we’ve lost something irreplaceable.
Right. Unlike New Orleans, which is of no cultural importance whatsoever. Especially when it comes to music or cuisine.
What about the Smith Island cake? It’s the official state dessert. And it’s delicious, I might add.
Thing is, Isabel isn’t the only character with an inner voice she’d like to hit the mute button on. Carrie also has a voice like that. It is the voice of the part of her that is constantly calculating her own advantage. She thinks of it as “the cold thing” or her “inner sociopath.” You can read all about it here.
It occurred to me to wonder if that voice should be in boldface too, since it is also egodystonic— that is, it’s something the character doesn’t like to think of as a part of her mind. After some thought, I decided against this.
One reason is that they’re two very different voices. One is deliberately unhelpful, the other helpful in a rather nasty way. The other reason is that Isabel’s inner critic rarely manifests itself in her behavior. Most of the other characters who know her would say that she’s prone to an excess of defensiveness, not realizing what it is she’s trying to defend herself against. Whereas Carrie sometimes chooses to act on the advice of her inner sociopath, and sometimes chooses not to. Basic existentialism says we are what we do, not what we think or intend.
If all this seems like way too much philosophizing for a question like this, well, welcome to the voices in my head.