So, I was sort of egged into a theoretical analysis on BBF that amused me.
The problem was this. As a passed-hand Dealer, you hear partner open 1D in third seat and a 3H overcall by RHO. With Axx-x-Jxx-AQxxxx (why you did not open is a mystery, but the challenge has these conditions), you must (for the fun of the argument) respond by bidding 3NT. The challenge is to explain why 3NT is the right call.
So, thinking through theory, I found a plausible explanation (perhaps). The fun of the challenge is to think through principles of theory and to reach this conclusion in a "somewhat" supportable manner.
My thinking went along these lines. First, with spades, I would double or bid them. So, spade-based hands are out.
Second, to commit us to anything at this level, I must have a landing zone. This usually means diamond support, for the obvious reason.
So, it seemed that there were a few possible scenarios to consider here.
I might have long diamonds and a heart control. But, with that hand, it seems that I would have opened 1D or 2D (weak). Thus, the "I just have lots of diamonds and a heart control" scenario seems reasonably out. Granted, I might have just five diamonds, and a near maximum, but I open 1D with 11 HCP, so what am I getting all excited about on lesser values?
The other alternative is reached by considering what a 4C call would mean. IMO, introducing a new suit at the four-level, as a passed hand, is absurd if it stands on its own. Rather, 4C would only logically make sense as a fit non-jump (clubs, with diamond support).
If we assume that 4C means this, the obvious downside to bidding 4C as a fit non-jump is that you just bypassed 3NT, which might be the ideal end contract.
3NT would make some theoretical sense, then, as a surrogate for a fit non-jump with clubs, getting at or below 3NT to allow partner, with the right hand, to convert to 3NT or to pass as that conversion. If nothing else makes sense other than a "surrogate fit non-jump 3NT" call, then clearly (lol) that is what 3NT shows. Challenge met.
Now, this is all somewhat nonsensical (or is it?!?!?). But, the fun was in the challenge and using actual theory concerns to reach the required (by the challenge) result.
So, for the sake of argument, I then started thinking. Is there something to be said for actually using a fit non-jump surrogate in some sequences? If the idea has some merit this seems like a reasonable sequence to use it. Maybe there are other situations. A recent discussion on BBF suggested after P-P-1H-(2NT)-? that 3D operate as what could be called a surrogate fit non-jump, meaning heart support with spades (Justin Lall mentioned this). The surrogate is needed because 3S bypasses 3H.
Other of these beasts might be out there.