Grammatical pitfalls when ‘everyone’ is the antecedent

I THOUGHT I was being presented with a red herring when I received an e-mail a few days ago from a Quezon City-based lawyer who made this observation: “In his recent State of the Union address, US President Barack Obama said: ‘Everyone must do their share...’ That is now very common. We hear a lot about ‘everyone’ being asked to do ‘their’ part in nation-building, etc. And what’s the deal with ‘between you and I’?”

Evidently, Atty. Stephen Monsanto meant to say that President Obama could have said “Everyone must do his or her share” instead, but didn’t because even if that usage is grammatically airtight, the preferred option now is the plural adjective “their” for such constructions even if it’s grammatically faulty.