Many stories are told from multiple points of views, from opposing viewpoints in a romance to different members of a heist team. But how do you make each character sound unique, not just in dialog but also in their narrative prose?
In a movies we tell characters apart by comparing visuals - hair color, hair cut, skin tone, fashion. In audio we tell character apart by sound - accents, pitch, if they’re breathy or raspy. And so in text authors have two ways to distinguish characters (other than saying their name all the time) - word choice and grammar.
Characters will be compared against each other - the one who swears and the one who doesn’t, the one who uses small words versus big words - and so consider these aspects of word choice and grammar to develop a unique way for each character to think and speak.
Swear words - do they use them? do they only use certain ones? do they only swear using the names of classic literature?
Sentence length - short fragments? Or perhaps they are overly fond of using longer sentences?
Formality - do they speak in slang? or do they use particular, posh language? Wanna go out? vs Can I invite you to dinner?
Metaphors - are a character’s thoughts slow blooming, or buffering? Character interest should guide the metaphors and similes they use, and this difference does double duty at giving character’s a unique voice and showing character personality.
High/Low Context - high context and low context are terms that describe cultures, including how they communicate. High context means a character is rarely direct and communication is through a combination of nonverbal, personal, and social cues. Low context communication is very direct. This is the difference between someone asking for salt and someone saying the chicken is bland and expecting you to pass it unprompted. In prose, someone from a high context culture would also be paying more attention to body language and think throughout a conversation. A low context narrator might not insert action or thought beats in a dialogue.
Filler words - does, like, she speak with a lot of fillers? Or is she efficient? Adverbs can also be filler words. Honestly, Danny was really surprised she decided to go for it vs Danny was surprised she went for it.
Catch phrases - common in anime and hero stories, catch phrases don’t have to be the names of power moves. They can also be consistent ways a characters says hello, goodbye, or express excitement. Think Cyborg’s Booyah or The Tenth Doctor’s Allons-y.
Grammar structure - easier to do if a character is noted to not be speaking their native tongue or a device translation, but structure should be restricted to dialogue and not prose to prevent reader confusion. Think a character who only speaks in the passive voice, or who ‘has hunger’ instead of ‘is hungry’.
Nicknames - whether or not a character uses nicknames at all can be a differentiator, but also the use of a nickname no one else uses. A dad and mom might have different names for their child. The use of a specific nickname can also be a dialogue shorthand to indicate who’s speaking. “So there I was, clinging to the pier support-” “Little Wing!” “Shut it.”
What they notice - different people notice different things and that should be reflected in prose to separate the voices. For example, the main character might walk into a bar and notice the patrons, but his best friend is busy checking out the decor. And some characters notice nothing.
While some of these tricks work better in dialogue or and other in prose, they work together to develop a distinct way a character communicates both when speak and when ‘thinking’ or narrating the text.