I've been wondering about voice for a while. Being a linguist, I know a lot about language, and teaching writing I've started to figure out what makes writing effective. But voice has always been unquantifiable. People say everyone has voice. What that means, I think, on a basic level, is that everyone has a certain set of words that are their go-to words, they have a certain idea of what makes a sentence flow. It often reflects the way they speak - where they put adverbs, whether they use lots of rhetorical questions. But there are three pits you can fall into with voice.
1) An inconsistent voice.
2) A sloppily executed voice
3) The wrong voice for the story.
If voice is something that everyone has naturally and everyone has only one, then how can there be a wrong voice? Am I saying that some people can't write certain types of books because they have the wrong voice? No.
When we speak we frequently exploit varying registers. If you're speaking to your little brother, you're not going to speak to him in the same way you would speak to your boss, right? (Unless your little brother is your boss, in which case, I'm sorry.) And if you do speak to your boss in the same way you spoke to your little brother, you might get fired. These registers are basically systems of preferences.
Little brother: Prefer 'hey you!' Imperative voice. Casual language. Slang. 'or else!' Short sentences.
Boss: Prefer 'please' Subjunctives like 'would, could, might.' Formal language. No slang. 'do you think...?' Longer sentences.
We can switch between them easily!
In writing, though, register becomes more complex and tentative. You don't have a person that you're directing it to, so it's harder to make choices. And often you're writing in a certain style.
Style in essay writing is a lot like register. You consider who your audience is. You ask, do we want to impress them or to befriend them? You write.
It's harder to figure out what's right for a novel. An MG voice isn't the same as an adult voice, but a comedic voice isn't the same as a mythic voice either. Choosing a style is not just choosing an audience, but figuring out the feel that you want your writing to have.
The problem comes when you actually try to write it. We all have registers for friends vs. teachers, but we don't necessarily have a particular register ready to address the emperor, or to talk to baby ducklings. We don't all have a gothic style at our fingertips, or even a comedic style. And if we can't control the style we're writing in, things start to fall apart.
When agents and editors say voice, what they mean is this:
Voice - The consistent and correct exploitation of a style.
The way your style will come out is directly linked to your experience of language. That's why reading a lot of the type of voice you want to master can be helpful. You learn and then you make generalizations. "Use long sentences." "Use creepy words like 'lacework' and 'groan.'" But unless you only read those books and words from the age of two and never speak to anyone else, you're not going to mimic it exactly. It's going to build another layer onto your own language. Your own language is the source, is the bricks. Your language will merge with this new style to create a voice.
But that's not enough to create Voice. It has to be consistent. Part of that is controlling the style (rather than letting the style control you). Part of that is controlling the perspective, making sure that you know who you're talking to and what your relative positions are (social positions, but also physical and temporal positions.) Languages take note of who is speaking, who they're speaking to, when they're speaking, when what they're speaking about occurred in relation to the speaking, and where they are in regards to the action, as well as tons of other things. Controlling the perspective (a lot of this goes into the POV) is part of controlling your style.
If you can't control the style we often end up with sloppy execution. Sloppy execution suggests not paying attention to the details. And there are a lot of details! Are you referring to your reader as 'you' or 'one?' Are you referring to your reader at all? Have you forgotten what perspective your narrator is relating the narrative from? Slipping in a modern slangy term into a historical, slipping in an old-fashioned word into a modern story. Using the same structures repetitively without any clear reason. Readers have to get used to writing styles. A sudden shift in syntax can be jarring. If you just got used to having post verbal parenthetical adverbs to suggest contrast, "John went, surprisingly, to the store." and then suddenly you shift to 'but' clauses instead, it's going to give the reader whiplash. "John went to the store, but it was unexpected."
Styles don't have to be dramatic. You might say, simply, I'm going to write in a colloquial style, as if I were telling this story to a friend. But which friend, when, for what purpose? All of these things go into your voice. Every day, we speak in many registers. We have the ability to write in many styles. But we choose register based on context. Choosing a style is conscious - and often, a whole lot more fun. But pulling off the style - that's voice.