"Grammar: “Different from,” almost never “different than” June 10, 2009 Posted by federalist in Language.
Tags: different from, different than, different to
Different is an adjective form of the verb to differ.
If one thing differs from another then we can say “One thing is different from another.”
We cannot say “One thing is different than another” any more than “One thing differs than another.”
Generally different from is correct and different than is not.
But of course one thing can differ more than another, in which case we can say, “One thing is more different than another.” It is correct to use different than when different is part of a comparative adjective.
The strange exception to the general rule: Use different than when different modifies an elliptical clause (i.e., a clause in which words have been omitted). For example, “The path follows a different route than the map shows.”
According to this page, the Collins Cobuild Bank of English shows that Americans have developed a tendency to butcher these rules in normal speech. Meanwhile, the British are prone to use the absolutely incorrect formulation different to.