[Stephen Tu]

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Given the common style where 2c is often some weakish 4 cd, possibly even 3 cd suit, shouldn't North bid 2h instead of 3c? Conserves space, can always support clubs over 2nt or 2s.

[barmar]

I agree, that's how I would bid the hand.

However, notice that 3♣ didn't say 3- H, so it doesn't deny hearts. You can bid 3♥ over 3♣, and this shows "5+ C; 4+ H; 14+ total points; forcing to 3N", a perfect description of your hand. And then GIB will bid 4♥, which shows "4+ C; 4+ H; 5+ S; 11+ HCP; 12-16 total points", also a perfect description of its hand. Yes, you're a level higher when you discover your ♥ fit, but you have more information -- you'll never discover the double fit if GIB bids 2♥.

In contrast, the auction 1♠ 2♣ 2♥ 2NT 3♣ only promises 3+ ♣, not 4. And it can't support clubs over 2♠ -- that shows 3-card ♠ support, and 3♣ would then be a slam try.

[Stephen Tu]

But we want GIB to bid like a normal person, and for normal people, 3c denies 4 hearts. And you don't bid 3h over 3c holding a good diamond stopper catering for the 4-4 heart fit, unless you like playing dicy 5c contracts rather than cold 3nt contracts opposite the far more common 5224 and 5314 shapes. 3h isn't a "perfect description" of my hand, opposite a human partner, because strongly implies no diamond stopper.

[georgi]

3♣ followed by 3♥ might be better description for each of both hands as you know 5+ from each hand and certain 4+4+ fit ( in case you don't have opening major fit ). How you would distinguish 5404 or 5413 has opener after:

1♠ - 2♣
2♥ - 2NT
3♣

3♦ instead of 2NT makes things even more dangerous for opener cornered to evaluate whether your Jxxx or xxxx might be a stopper or 5♣ is pretty much safer.

Maybe with ♥AKxx and ♣xxxx things could be different, but it's always matter of opinions. And everyone could have been right.

[Stephen Tu]

There's overwhelming human expert consensus to prioritize bidding hearts over clubs on this auction. GIB should conform to human consensus when things are matter of opinion. 3c follow by 3h is not better description when the bids in principle only show stopper not suit.

Distinguishing between 5404/5413 is arguably not all that important. With solid diamond stop a min responder can bid 3nt and opener with also min should respect it. With lesser diamonds responder will do something else, and opener can just be more aggressive with 5404 than 5413 when it decides between 5c/6c. With a slam invitational 5404 over 3nt it can try 4c again to try for slam.

Over 1s-2c-2h-3d, which should be 4sf artificial IMO, not natural diamonds (just bid 2nt), then easy 4c/5c bids with 5404 shape.