Why is " I" not " me" required in this comparative clause? [duplicate]

You find both accusative pronouns (me/him/her/them) and nominative pronouns (I/he/she/they) in this syntactic position in standard English. The forms with the nominal genitive pronouns (mine/yours/hers etc.) are a red herring because they stand for something possessed rather than the person themself.

The traditional rule for comparison with a person is that you must use nominative. However, according to my research, accusative is more common.

I searched the Corpus of Contemporary American English for this syntactic structure, followed by a comma or a period to ensure we are not looking for cases like faster than he is, with a verb following the pronoun, in which case nominative is obligatory.

There were 1046 results for the accusative pronouns and 450 for nominative pronouns, more than 2 to 1 in favor of accusative pronouns—the “traditionally wrong” form. Both forms are standard, so my advice to a writer choosing between these forms is to consider that the “traditionally correct” form is unimpeachably correct but a bit formal. Choose the form that best matches tone and formality level of your writing.

For the curious, the queries looked like this:

[jjr*] than me|him|her|us|them .|,
[jjr*] than I|he|she|we|they .|,

where[jjr*] means any comparative adjective.

Update 2011-05-23

Using the new Google Book Corpus search, I was able to construct a Google ngrams-like graph comparing these usages over time, using these two queries: accusative, nominative:

As you can see, until the late 1980s, the formal usage was more common than the informal usage. Since then, however, accusative has very rapidly eclipsed nominative, even in this corpus, which represents professionally published works.

Ah, you've stumbled onto a controversy even the experts haven't completely settled. It all depends on whether you think than is a conjunction or a preposition.

First, remember that "I" is always a subject, and "me" is always an object.

If than is a conjunction, then it's joining two complete sentences, and the "am" that you mention is the implied predicate of that sentence. In that case, "I" is the correct subject. (Except where's the comma you normally would use before an and that joins two sentences?)

If than is a preposition, then there is a prepositional phrase, which needs an object, not a subject. In that case, "me" is the correct pronoun.

Consensus seems to be on the side of the "conjunctionists" -- even if common usage isn't. I always use than like a conjunction in writing, but in speaking, I usually find myself using it as a preposition because it feels more natural somehow. So I guess I have a foot in both camps. ;)

There's an excellent discussion of this at Grammar Girl's blog.