an in Burbank recently came across an article in which a speaker was quoted as saying that a mother is of "the opposite sex than" her son. The speaker gets an A in anatomy, but Dan wouldn't grade the speaker as well on his English.
"I've been grinding my teeth at the increasing use of 'different than,'" Dan wrote. "I understand 'than' to indicate hierarchy — taller than, dumber than, less grammatically correct than — while 'different' sets up an 'apples and oranges' comparison on the same plane, and so comes out 'different from.' And I don't even want to begin to understand the thought process involved in 'opposite . . . than.'"
"Than" is one of those words we use every day without thinking about it. Then, one day, someone calls it into question and we realize it's not so simple.
"'Different than' is often considered inferior to 'different from,'" writes Bryan Garner in "Garner's Modern American Usage." "The problem is that 'than' should follow a comparative adjective (e.g., larger than, sooner than, etc.), and 'different' is not comparative."
"Comparative" here doesn't mean any word used to make a comparison. It means something more specific. Remember learning in school about comparatives and superlatives? Comparatives either end in "er" or start with "more" — taller, faster, more intelligent — while superlatives end in "est" or start with "most — tallest, fastest, most intelligent. That's what Garner means by comparatives.
So "taller than" makes sense, but "different than" does not. That's why I advise people to choose "different from" over "different than." But, of course, it's not always so simple. Look at the sentence "Tom has a bigger house than we do." Replace "than" with "from" and you get total nonsense: "Tom has a bigger house from we do."
"Than" is most often a conjunction, and subordinating conjunctions like "than" usually introduce simple clauses — complete with a subject and a verb. You work harder than he does. Diamonds cost more than pearls cost. True, we sometimes shorten those forms: Diamonds cost more than pearls. But that's just because we're leaving the second verb implied. Even then, the idea following "than" is still a complete clause.
So it seems to me that "Bananas are different from plantains" makes sense because the object of the preposition "from" is a noun. And "Bananas taste different than plantains (taste)" casts "than" in a true role of a conjunction, introducing a whole subordinate clause.
But that's just a casual analysis by one observer of highly questionable expertise. If you want a final verdict on whether "different than" is officially wrong, you should turn to a higher authority.
"The commonly expressed view that 'different' should only be followed by 'from' and never by 'to' or 'than' is not supportable in the face of past and present evidence or of logic," writes "Fowler's Modern English Usage."
But I think even Fowler and Garner would agree that because "different from" is more logical, it should be your first choice and you should abandon it only when it fails you completely.