Originally Posted by
ralfp
The closest thing to a rule is that F has no middle seats, while business may have middle seats (see United's 2-2-2 domestic F vs. 2-3-2 business on their 777s).
Of course someone will find an exception to this "rule".
Another "rule" is that if you buy an international business ticket with a connection to a different domestic US carrier, you will be sitting in coach, as you don't have a first class ticket.
That's certainly not the case, in fact I've always flown into the US on a business ticket and always flown the domestic segment in what is comically referred to as first class.