As you know, there are lots of rules in English grammar and "different from" and "different than" are not exceptions. These two expressions have been used - almost interchangeably - for hundreds of years. There are, however, subtle differences in their use.

For example, "different from" is the preferred expression when introducing a phrase. Nonetheless, "different than" can also be used in the same phrase and leave the phrase's meaning unaffected. Here's an example:

A Londoner's accent is "different from" that of a Glaswegian's accent.

A Londoner's accent is "different than" that of a Glaswegian's accent.

As you can see, either expression is fine.

"Different than" is the preferred expression to use when introducing a clause, but you can still use "different from" if you simply add a few more words into the sentence. Let's see an example:

The street led to a "different" road "than" the map indicated.

The street led to a "different" road "from" the one the map indicated

OR: The street led to a "different" road "from" the one indicated on the map.

So, either expression is correct as long as you bear in mind that you will sometimes need to use additional words.

We can also use the expressions as adverbs. Adverbs are simply words that modify verbs and adjectives and they usually (but not always) end in "ly", as in really, quickly, quietly etc. The adverb of "different" is "differently" and there are certain ways that you can use "differently than" and "differently from". You use "differently than" with a clause following and you can use "differently from" in the same way as long as you use extra words. Here are some examples:

She looked "differently than" she had hoped after getting her hair cut and styled.

She looked "differently from" what she had hope after getting her hair cut and styled.

So, as you can see, both expressions are correct, but sometimes additional words needs to be inserted into the sentence in order to be grammatically correct. It seems that both expressions can be used pretty much interchangeably, as has been the case for around three hundred years, but you need to be aware of the subtle differences between them. And remember that these phrases are correct whereas "different to" is not the best choice to use in a sentence! It's a common mistake to make when comparing two or more things, but if you want your work to be taken seriously, stick to "different than" or "different from".

KJ Hutchings is the owner of KJ Language Services, providing proofreading, editing and writing services to businesses and students, in particular those who use English as a second language. For more information, visit her site at: http://www.kjlanguageservices.com/