It’s a construction that stops every copyeditor at least once in their career, and it’s been argued about for more than a century: What type of pronoun follows than at the end of a sentence? Should it be “Stefan is more brooding than I” or “Stefan is more brooding than me”?
The same problem can arise with as/as constructions (“Caroline will never be as strong as he or him.”), like (“No one casts a location spell like she or her.”), and other connective words.
As with so many editorial dilemmas, the solution — inasmuch as there is one — isn’t strictly grammatical. Editing is not math, in which a set of inputs leads inevitably to one output. There are a few elements to consider:
The Case for Traditional Grammar
The problems arise because than and its syntactical ilk can be used as both a conjunction (“There’s more vervain here than Damon can stand.”) and a preposition (“Klaus would rather have blood than tequila.”).
Historically, grammarians have called for a personal pronoun in the nominative (subject) case to follow than in such a comparative statement: “Tyler got even angrier than she.” In this construction, than is analyzed as a conjunction, with the personal pronoun acting as the subject of an understood clause. With the understood parts of the clause included, the sentence would be “Tyler got even angrier than she got.”
Both history and common usage are on the side of using the nominative pronoun after than, and you can fairly bet that it’s what is expected in formal written English and serious academic prose. But…
The Case for Register
The hypercorrectness of a sentence like “The Mikaelsons are so much older than I” can sound snooty or overly formal, making it a bad fit for some registers. In informal or colloquial English, than can be analyzed as a preposition instead, with the personal pronoun that follows it in the objective case: “Bonnie knows more magic than him.” This is a pretty standard construction for informal registers.
It also eliminates the oddness when that final pronoun is a third-person plural: “Alaric alone has staked more vampires than they.” In an informal register, the objective case will suffice: “Alaric alone has staked more vampires than them.” In a formal register, the verb that was understood is usually included: “Alaric alone has staked more vampires than they have.”
But a “than they” sentence is grammatically equivalent to a “than he” sentence.
Using than as a preposition can lead to some confusion, too. Consider the sentence “Katherine likes Damon more than him.” It could be interpreted to mean either that Katherine likes Damon more than she likes the second, unnamed male (presumably Stefan), or that she likes Damon more than the unnamed male likes Damon. Unless ambiguity is your aim, sentences like this need a little editing for clarity.
The Pair We Don’t Talk About
To some strict grammarians (perhaps that’s you?), the analysis of than as a preposition might seem more like a rationalization to justify a usage someone already wants to use than an honest grammatical interpretation. Those grammarians see than only as a conjunction in such a construction, and so a nominative pronoun should be used consistently. But here’s another twist: Discussions (read blog posts) about than inevitably focus on the personal pronouns I/me, he/him, and she/her. There’s another pair to consider: who/whom.
Consider which of that pair you would put into this question: “Matt is hotter than _____?” In my experience (YMMV), “than whom” is one of the very few constructions in which whom sounds and feels correct. But whom is the objective case here, which means than must be interpreted as a preposition. If than were interpreted as a conjunction, it would call for the nominative case: “Matt is hotter than who?” Ironically, the latter form sounds more unlearned, even though it relies on the stricter and more traditional grammar of formal written English.
Grammar et al.
So what can we conclude from all this? Perhaps that grammar should not be the deciding factor when you’re trying to get the most out of a manuscript? Or that grammar is not some set of rules etched in stone forevermore? Or that grammar is a tool for good writing, not the judge of it?
Editors and other logophiles and wordsmiths can disagree — and often have — about all aspects of the English language, from the placement of adverbs to the plural of syllabus. This than I vs. than me argument has been occupying wordly circles for literal centuries — during which time, both constructions have been used by writers we consider masters of the English language — and I don’t expect it to end any time soon.
Meanwhile, we copyeditors still have to work, which means we have to make decisions and stand by them. To make that decision between, say, “Andy has watched more episodes of Vampire Diaries than I” and “Andy has watched more episodes of Vampire Diaries than me,” we might start with grammar, but we can’t stop there. There are other considerations.
Consider register. Consider the flow and the pacing. Consider the author’s voice and the audience’s expectations. Then decide.
All of these elements are important to crafting text that really sings.