Third Suit Forcing

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What I describe here is, as best I can tell, very similar to the Bourke Relay. I'll call it Third Suit Forcing because I don't have access to an authoritative description of Bourke Relay, though I did find some discussion of it here and here. There's a related convention TSAR invented by Jeff Rubens which would be too esoteric for most partnerships.

The problem addressed is what to do after an auction like 1♦ - 1♠ - 2♦, where you need to explore further but don't have another suit to bid.

More generally the situation is where the opening bid is one of a suit, the response is one of another suit and opener makes a simple rebid of their suit at the 2-level. With this convention the cheapest available bid of a new suit by responder is an artificial game force and asks opener to further describe their hand. It is very similar to Fourth Suit Forcing.

Here are some examples of opener's third bid:

1♦    1♠
2♦    2♥    Third Suit Forcing
2♠          2 spades, no second suit
2NT         Natural, stoppers, likely singleton spade
3♣          Stopper or 4-card suit in clubs
3♦          Natural, not suitable for 2NT or 3♣
3♥          Natural, 4 hearts
3♠          3 spades

If the relay suit is above responder's suit the choices are a bit more limited:

1♦    1♥ 
2♦    2♠    Third Suit Forcing
2NT         Natural, stoppers, 1 or 2 hearts
3♣          Stopper or 4-card suit in clubs
3♦          Natural, not suitable for 2NT or 3♣
3♥          3 hearts
3♠          Natural, 4 spades

Playing Transfer Responses to One Club, the principles are the same:

1♣    1♥    Showing 4+ spades
2♣    2♦    Third Suit Forcing (opener has denied 3 spades)
2♥          Natural, 4 hearts
2♠          2 spades, no second suit
2NT         Natural, stoppers, likely singleton spade
3♣          Natural, not suitable for 2NT or 3♦
3♦          Stopper or 4-card suit in diamonds

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I recently learned there is also a nice article about this from 2015 on the Bridge Winners site. Curiously it has the same title as the one above.