I've unintentionally plagurized before. Often I plagurize before I've read the book I rip off because some ideas in fantasy are just too cool not to be thought of simultaneously, have a lot of cool variations, and are spread thin enough that you pick them up without even knowing it.
Por ejemplo: In one of my "lesser works,"
The Wizard of Silbay, I introduced a form of communication where
Wizards talk to each other through a device I'd thought up by combining modern instant messaging and
Myst linking
books, so I already had admited some "influence," but heck, you can't rip off a computer game. . . So, you write something in the book, you writing disappears, writing from the person with the other books appears.
A couple of months after I invented this device, but while I was still writing the same book, I finally got around to picking up the second Harry Potter book (I'm not really a fan of these, but I was still babysitting occasionally at the time so every so often I'd get a copy shoved at me by an enthusiastic pre-teen). I thought, "Oh dang, this is pretty similar. . .but wait, the diary is actually alive and my book is just a link between two persons. That's OK."
Still, when I let a creative writing class read the first chapter (I only used the device in the first chapter) of the novel and waited to see if they though I'd ripped off Rowling or Cyan (whoever does
Myst.). Instead, one lady in the class asked if I'd borrowed it off a fantasy book I'd never read and scarcely heard of (I want to say it was
Sword of S????, which I think is Terry Goodkind, but I can't remember for sure.).
A
lot of fantasy devices are similar. How many versions of mysterious, silent characters in dark cloaks who don't really like the sun are there? I know I've used it, because it is just so much scarier to be chased by some presence that could be anything or nothing at all than some monster with three eyes and six horns or a head of a skull or whatever you want to paint in. That's where we get
Nazgul and RaZac (sp?) and those shade thingies from Robert Jordan (were they shades or mages or what?). In fact, these things are always less scary once they've been "de-cloaked."