In the sentence “Alex liked Nancy, with whom he shared his Snickers bar with” only one “with” is needed—eliminate either one. Look out for similarly duplicated prepositions.

Incidentally, an often-cited example of this pattern is from Paul McCartney’s Live and Let Die: “this ever-changing world in which we live in”; but if you listen closely, you’ll hear instead a quite correct “this ever-changing world in which we’re livin’.” Americans have a hard time hearing the soft British “R” in “we’re.”

List of errors