A discussion on BBF interested me.
Partner passes as Dealer (not vulnerable), pass, and you open One Club. LHO overcalls a strong 1NT, and partner bids 2H.
Now, for my part, this sequence is often discussed and shows five hearts with five clubs.
But, the interesting part was analyzing what it would mean logically if the auction were not discussed and if no general agreements for this sort of situation were available. In other words, what is the LOGIC of the situation?
You start with one principle for any and all analyses. Partner is sane. I know, this is dubious, but you have to start somewhere in the hypo. Sanity implies something to say and safety saying it. A landing zone should be contemplated for dangerous action.
One aspect of the analysis is partner's predisposition and style in making weak two's. If strict, maybe 2H shows cruddy but long hearts. But, if cruddy but long hearts is just fine, then that's out.
The second rule: Partner cannot have later what he denied earlier. This is not like Poker. You cannot hand three cards to Dealer and ask for three new cards. You start with what you end with. So, bids are defined by prior actions and by prior inaction.
When would partner NOT open 2H but be safe bidding 2H?
One option is that partner's hearts are as good as he says. If he has that, he was good enough to open 2H. So, he has a flaw. The likely flaw is holding four spades also. So, one logical interpretation is "six hearts with four spades."
Another option is that 2H describes a hand with insufficient hearts to open 2H (hence five) but a logical landing zone. That might mean a "DONT" or Brozel approach (hearts and spades), a Cappelletti approach (hearts and a minor), or a "fit bid" approach (hearts and clubs).
Which is used might be a function of discussion, but it might be a result of applying parallel structure (we use Cappelletti normally, so Cappelletti makes sense here). It might be a function of percentages (6H/4S makes sense, but the two-suited situations occur more frequently). It might be a function of limited space (Cappelletti makes sense IF 2C agrees clubs, which it does, but DONT and Brozel do not because we need double for penalty, for example). It might even be a function of the opening bid context (fit bids making sense if the minor is real, but capp if the minor is short or Nebulous).