For example, someone might state the truism that "women are different than men." But that would be bad grammar. The way it should be stated is "women are different from men."
Well, if instead of using the word different you stated the truism using the word differ, the reason becomes obvious. You wouldn't say "women differ than men." You would say "women differ from men." Therefore, you should say "women are different from men."
What's the difference between from and than?
The word than, like from, is a preposition. It usually follows an adjective when drawing a specific contrast between people, things, or conditions.
- Florida is hotter than Minnesota.
- Trees are bigger than bugs.
- Cars are faster than tricycles.
And here's where the English language is once again...different from many others. If a clause (instead of just a noun or pronoun) follows the word different, go ahead and use than.
For instance, it would be correct to say, "Writing about grammar is different than I expected it to be."