This parallel / alternate arguement is a funny one. It's true that all sci-fi / fantasy worlds could be considered alternate, but not all can be parallel. The first criteria that must be met is that in a parallel world book a character must travel between two worlds during points in the book. Secondly, I would think that parallel worlds must be linked together in some way other than the one character being able to travel between them.
Using these simple criteria (and I do mean simple, there must be a better explanation out there somewhere) we can start to put order to some of the books mentioned. Alice, in Lewis Carroll's books, does travel from one world to another. However, besides her ability to travel between them, Wonderland and Victorian England have no similarities.
The Blue Adept series, on the other hand, has two worlds that slolwy become dependent on each other. The success or failure of the character in one world greatly effects his success in the other world.
On another note, using this classification system I must admit that The Man in the High Castle would not be classified as an alternate world book. Really it is an alternate world of OUR world, and not of a any character within the story. However, it still is an amazing read.
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There are two things I always forget, they are . . . there are three things I always forget . . .