I really can't dissent from Alain's essay; it all makes a lot of sense. A couple of observations:
I was once looking through a compendium of Robert Mapplethorpe's nastier photos with a couple of people, and one asked, "Why would he photograph anything like that?" and the other guy, who was an architecture critic and one of the smarter people I know, answered, "Because that's what he's interested in."
An awful lot of people on internet forums seem to have an interest in cameras and sensors and in being "a pro," but they really have no passion; I personally think the thing that makes a style, is passion, and it has to be there before the camera. One of the reasons that Weston took terrific, ground-breaking nudes is that he was very interested in the nude lady. I don't like Sylvia Plachy at all, but I could pick out one of her pictures from hundreds of others, from across the street. The same with Ansel Adams (who had a passion, I think, for clear air), Jock Sturgis, Diane Arbus, Paul Caponigro, and all the others. On the other hand, you have somebody like Lee Miller, about whom there have been a number of recent books: she took some good war photos during WWII, and some decent fashion photos, and some okay art-type photos with Man Ray, and she even posed nude for some really glorious photos by Man Ray...but unlike Man Ray, she didn't seem to have a style. I have looked at a lot of Lee Miller photos, but, going on style, I couldn't pick one, for sure, from a choice of two.
The thing about any good artist who has a style is that cameras, sensors or film, photographer tricks, etc. -- or paint for painters, or stone for sculptors, or typewriters for writers -- are a relatively trivial aspect of the work. You have to be fascinated by a subject matter, or you're SOL. Try to think of a guy who was a great war photographer, and then became a great portrait artist, and then a great landscape photographer, and then a great figure artist, and then a great news photographer..and you can't think of any, because because guys who are *really* good are more interested in a subject matter than in a career as a photographer (or painter or writer). Despite themselves, they keep coming back to that subject matter. They can't resist it; it's a drug.
To be fairly good or competent at everything is to be a pro; to have a laser-like fixation on one subject matter that you can't get away from, and to then try to get at that subject from every possible angle, and to lie awake at nights trying to think how to get at it better...that's an artist.
You can get to be a pro by going to school long enough; artists don't need no stinkin' schools.
One of the things that I sense about a lot of people on photography forums is that they may have wide interests -- they're intellectuals of a technical kind -- and they sort of like the cool image that they think photographers have, or the idea of themselves as artists, and maybe they'll get to jump a model sometime, or get a neat photography hat, but they're really actors, who are mostly interested in themselves and their personal self-images. If that's the case, well, most people might do best to take pictures of themselves (although that artistic niche is already pretty fully occupied), and who knows, it might turn out to be art.
(And I hasten to say that I think there are a number of serious artists on this board.)
In any case, I believe that style follows passion, and rarely or never runs the other way. If you don't have the passion, you'll never be *really* good as an artist. If you do, then you've got a shot at being *really* good; and if you persist in the work, a style will emerge spontaneously and inevitably, as a result of the passion.
JC