I'm working on my novel and I was wondering if nicknames are alright to use when a character isn't speaking. EX: “Sam was having a really intense vision and I was stupid enough to scare her out of it,” Morgan replied sheepishly. Sam didn’t see this as an excuse in any way, shape or form. “Are you sure you’re alright?” she said in a choked voice. In the second paragraph- is using "Sam" alright or do I need to switch it to her full name (Samantha)?
Heck, if anything you'll see "Sam" more often than "Samantha." My theory is it's because writers figure they can get another two thousand miles out of their keyboard when they're writing the name every other paragraph in a 900 page book. There's no problem with that at all. The only question is do you want the reader to think of her as "Sam" or "Samantha?" They carry different connotations after all.
Whatever fits better with her character. I'm reading a story right now about a man named Thomas. At the beginning, he was most often referred to as Tom, but as the story progressed and his character went under a drastic change, even the other characters stopped calling him Tom.
I think that shortened OR diminutive versions of the character's real name, e.g. Sam OR Sammy are fine in the narrative if they are what s/he are known as. A real nickname like 'Scarface' or something would be confusing if it were to be used interchangably with the character's real name, unless it's the only name given for him/her, OR if the character flits through without his/her name being given, e.g. 'His fingers were as thick and clumsy on the trigger as bananas...' Later on: 'Banana Fingers gave me a threatening look.' etc.
Why would it be a problem? It's certainly fine in neutral narrative to use the name the reader would recognize and be comfortable with. In cracter-driven narration, you should refer to the character in the way your POV character would, whether that be a nickname or a more formal appelation.
