I found a writing skills question in Barron's PSAT test guide that was confusing to me.
Mary is as fast as, if not faster than, anyone in her class and should be on the team.
The book states that the sentence is erroneous and should be changed to:
Mary is as fast as, if not faster than, anyone else in her class and should be on the team.
Why is it necessary to use the word else?
It's not: the book is incorrect.
The issue they have with the sentence is a logic/math one, not an English one: she cannot be faster than everyone in her class, since she's not faster than herself. However, the use of as fast as obviates that problem: she is as fast as herself. So the sentence is fine without else (though I'd unitalicize the sentence).
To me, the "if not faster than" part of the sentence seems unnecessary, since idiomatically "as fast as anyone" means "at least as fast as every person" [in the named group], which implicitly includes the high likelihood (given that all persons in the group probably aren't exactly equal in speed) of being "faster than at least some persons" as well as the possibility of being "faster than every [other] person." Thus, "Mary is as fast as anyone on the track team" means "Mary is at least as fast as every person on the track team." Both of these sentences, however, carry the strong suggestion that Mary is not on the track team, since, if she were on it, the speaker could have made that point clear by changing "anyone" to "any other runner" or by adding "else" between "anyone" and "on."
Similarly, "Mary is as fast as anyone in her class" means "Mary is at least as fast as every person in her class." In this case, logically, the unmistakable inclusion of Mary in "her class" establishes an implicit "other" or "else" in the sentence comparable to the explicit "other" or "else" needed in my "on the track team" example. It follows that calling the sentence "Mary is as fast as anyone in her class" erroneous is unjustified. But the legitimacy of that version of the sentence hinges on the validity of a trivial assertion—that Mary is at least as fast as herself. What makes the speaker's assertion about Mary's speed worth making isn't the matchup between Mary and herself but the matchup between her and every other person in the class.
Consequently, if you asked not whether "Mary is as fast as anyone in her class" is wrong and "Mary is as fast as anyone else in her class" is right, but whether "Mary is as fast as anyone else in her class" is preferable to "Mary is as fast as anyone in her class," I would say that it is, because it excludes a comparison (between Mary and herself) that no one cares about.
Then again, perhaps Mary is the class's pet king snake. If so, Mary isn't an "anyone" but an "anything, " in which case "Mary is as fast as anyone in her class" is correct and "Mary is as fast as anyone else in her class" is simply wrong.
