Superlative vs. Comparative – Getting all grammar-y!

So I acknowledge that I am sort of uptight about grammar (which I get from my dad), so I’m usually surprised and a bit disappointed in myself when someone corrects my grammar. So recently I had a little text convo with my parents where I described my 6-year-old as the baby’s “oldest sister” (she has two sisters, both older than she is). My dad texted back, “older.” And I said, “isn’t it ‘oldest’ so it can be clear which sister I’m talking about?” He said no, so I had to look it up.

Apparently, according to traditional grammar rules, my dad is right: the superlative form (-est) is reserved for comparing groups of three or more. Since I was speaking of only two of my girls, the comparative form (-er) would have been more appropriate.

Really, I should have known my dad was right; he usually is about these things. I just don’t like to be corrected.

That said, this seems to be one of those rules that is frequently broken – so now it’s more of a “rule.” There are discussion boards galore of people going back and forth trying to figure out when to use the superlative vs. the comparative, and really my original way of saying it has become pretty common in spoken English. I even double checked The Elephants of Style (my review here) to see what Bill Walsh has to say about it, but it’s actually not covered in the book.

Basically, I’m left with this: The superlative should be reserved for comparisons among groups of three or more items; however, that will sometimes lead to confusion, and so many people are going to choose clarity over grammatical-correctness and break the rule.

Now that I have ineloquently shown myself to be a HUGE grammar nerd, please – weigh in! Tell me what YOU think!