Consider the two sentences below. They are almost identical, except for one word:
A Labrador is different from a Golden Retriever.
A Labrador is different than a Golden Retriever.
Potentially, one of those sentences sounded like nails on a chalkboard to you. On the other hand, both might sound fine to your ear. Whichever way you feel, when considering different from or than you are probably wondering, “Is one of those grammatically incorrect?”
The answer is a resounding, “kind of…”
The Meaning of Different From
From is a preposition. Prepositions show the placement of one word in a sentence relative to something else. This placement could be physical or figurative. In the case of from, this preposition indicates either.
Physically, a Labrador could be far from a vacuum cleaner. Figuratively, the dog could be free from worry. Different indicates an essential state of being, and from qualifies this state relative to something else. A Labrador is different. More specifically, it is different from a Golden Retriever.
The Meaning of Different Than
Does than function similarly as a preposition? Not exactly.
When used as a preposition, than refers to an object of comparison. For example:
A Labrador is larger than a Pekinese.
Notice that the adjective larger is a comparative form. The preposition than becomes necessary in the sentence because the subject Labrador is being compared to something.
However, different is not generally a comparative adjective. So strictly speaking, than doesn’t quite fit the bill. In fact, many English language guides advise that different than is wholly incorrect and should never be used.
We said that many English guides say different than is wrong, but others do not. Indeed, quite a few acknowledge that both different from and different than have found their way into standard usage. You can even find different than occasionally used in formal writing.
Even so, different from is much more commonly used. Plus, you might get some pushback from smarty-pants English majors if you use it in their presence.
When choosing between different from or than, the safe bet for these expressions is to always stick with different from. Granted, we don’t think either a Labrador or a Golden Retriever will try to correct you for using different than. In that regard, they are actually quite similar.