[RSClyde]

Can a partnership vary the meaning of bids based on which partner makes the call?
For example, say a pro and client. If the client bids something in a certain auction it is a transfer, if the pro bids makes the same call, it is natural. I can't find anything which addresses this directly. But is such a system allowed?

[jfnrl]

According to Law 40B2(a) last sentence, it is a matter of regulation.
"It may vary the general requirement that the meaning of a call or play shall not alter by reference to the member of the partnership by whom it is made (such a regulation must not restrict style and judgement, only method)."
It is forbidden in France :
"Article 135 - Obligations - Interdictions
1- Les deux joueurs d’une même paire doivent utiliser le même système et les mêmes conventions d’enchères et de jeu de la carte."
Google translation : "Article 135 - Obligations - Prohibitions
1- The two players of the same pair must use the same system and the same auction conventions and card play"

[RSClyde]

Thank you. What criteria might a regulating authority use on such a matter?

[blackshoe]

Whatever they like, I suppose.

[mycroft]

similarly, the ACBL. From the Alert Procedures (in the context of "two-system methods"):

Quote

As an aside, please note that it is not legal to vary your system during a session for subjective reasons, such as the skill level of the opponents which you happen to be playing at the time or which member of the partnership is making the call. You may, of course, alter your defenses in response to the opponents’ methods.

and similar, but not the same, in the EBU. From the Blue Book:

Quote

5 A 2 The members of a partnership must have the same bidding understandings and play the same
system of leads, signals and discards.

(However, 5 A 6 specifically allows playing different systems against different opponents, in any competition)

Most who do this do it explicitly to ban the "Client club" systems - systems designed to minimize the hands played by the (significantly?) weaker declarer.

[barmar]

In NABC midnight games, where half the room is expected to be drunk, the TDs don't generally enforce any system regulations, and we get lots of "creative" systems played by juniors. It used to be fairly common for expert juniors to play with cute caddies, and they played the "Caddy System", where all the caddy's bids were transfers because they had practically no idea how to play. This system seems to have faded out since BridgeMates came into regular use, so we have far fewer caddies (and the ones we have are mostly older).

[blackshoe]

Sometimes "progress" goes in the wrong direction.

[mycroft]

Way off topic.
And I ran a Crazy Bridge game last week (and went 4♠+3 playing 9 rounds of trump with my 5-3 fit, among other things¹) playing (when the rule on the hand made it make sense, of course) the other "standard system" in midnights, "Phantom Club". It was a lot of fun (and in a game where nobody cared and it didn't matter, I think we'd do it again), but equally illegal in the ACBL (although, oddly enough, mostly for "cuebid Drury by unpasssed hand").

Spoiler

For those who don't play the Midnights, the rule in Phantom Club is "as opener, bid as if RHO has opened 1♣ in front of you. Use 1♣ as double." Leading to the weirdest looks we got all day: 1♣ "Alert." "Yes?" "Either takeout of clubs, opening hand counting shape, or Really Big." "Takeout of clubs?" "Yes." "Okay..."

¹ The rule on that hand was "Bid and play the first 6 tricks normally. Record the tricks taken, and put those 6 tricks away. Play trick 7. Discard that trick and the rest of your hand, pick up the first 6 tricks and play them again as 8-13."