I got asked the other day about the difference between Voice and Style in fiction, and I got a bit stuck because I don't really know. I never use the word "style" in the context of writing because it's unhelpful, I said, whereas "voice" comes up often. Clearly I do think something, so in the time-honoured tradition of finding out what I think by seeing what I say, and aware that I'm giving two workshops at the York Festival of Writing, one on Find your Voice, and one on The Writer's Voices, so I'd better have worked it out by then, here goes.
OED's most relevant definitions of "style" include: "the characteristic manner of literary expression of a particular writer, school, period etc. ... a particular or characteristic way, form or technique of making or producing a thing... a manner of performance", which is all very well as far as it goes. But then there's "stylish", which is at once admiring (when it's about hats) and also reductive (when it's about painting or poetry), because "style" has come to mean how something's done, not what it is, and by extension it implies too much concern with How, and not enough with What. Even the judgement that a certain writer is a stylist can, unfairly, suggest that vital things about storytelling are sacrificed to the desire for a good-looking performance.
There's also the unattractive label "prose style" for the nuts and bolts of doing a decent writing job using your command (or lack of it) of vocabulary, syntax, grammar and prosody. That command is one of the things which makes your writing yours: it all comes down to your choices as an individual, about individual words. But should those choices be led by a conscious desire to alter your "characteristic manner of expression"? I'd suggest not. Yes, prose is nicer to read if the the shape and size of sentences vary, for example, but trying to do that from the outside leads to the absurdities and awkwardnesses of Elegant Variation. I think that's typical of what happens when you start from How rather than What, because you can't deal with a symptom well if you don't understand the cause. If what you're trying to say comes out awkward, flat, hackneyed or boring, then I'd suggest that rather than tinker with How, you think deeper and wider and harder about What you're trying to say: in the language of architecture (we're building bridges, don't forget) form should follow function, not dictate it, whether the function is a power station, a milking shed or a cathedral. I do mean "what" in the wide sense of course: not just the bones of the plot but the character of it and the characters in it, the atmosphere, the underlying ideas and spirit of the story. And then, as long as your command of the tools of your trade is good enough, and flexible enough - as long as you've learnt to get out of your own light - then the How will look after itself.
So what's Voice? I ruminated at greater length here, but to condense, for me, if Style is one manifestation of self, then Voice is formed by self. As humans we know that each person's voice is their own: the product of their language, their character, their mood, their actual physical construction. Which isn't to say that the only voice worth working with is unmediated self-expression. "Voice" also encompasses how different stories need different voices, as Nicola Morgan explores very well here. And, of course, it encompasses character's voices, not only in dialogue or when you have a character who acts as their own narrator, but when you're working in free indirect style and allowing characters' voices infect the narrative voice. The DNA of a novel's voice can't help but be yours, but how those genes are expressed (in the biological as well as the colloquial sense of the word) will be different for every offspring.
And then there's the definition of Voice as the thing that editors and agents are looking for above all else. That's partly because it's far harder to edit a compelling voice into a book which doesn't have one already than it is to make the plot, characters or prose work better. But it's chiefly because it's the voice to which readers respond on the first page, long before they've had a chance to find out what the plot is, or care about the characters experiencing it, or know anything about their world. The voice of a novel, if you like, is the product of the writer's How and their What. As such it's the closest a reader gets to the storyteller who has created it, and it's that human presence (however implicit) that the human reader connects with. Style is a one way thing: we admire the Ascot hat on the stranger's head. Voice is about discovering the person who's wearing it.