The artificial bid of the fourth suit, in the first two rounds of bidding, is forcing for one round and shows a chance of game. It is used when there is no preferable bid.
The responder bids the fourth suit to show 10+ points with no obvious second bid. The bid is not promising strength in the fourth suit. The opener must bid again.
The openers reply of 2NT shows less than 15 points with a stop in the fourth suit. With 15+ and a stop the bid is 3NT.
With no stop the opener must describe her hand more fully. If weak (less than 15 points) she rebids her first suit showing length (6+) or her second suit showing at least 5/5. This is not game forcing.
The responder can now pass, show 3 card support inviting game, bid game in one of her partner’s suits or NT. However, if the responder now bids at the three level in a different suit, showing strength, this is a game force.
If the opener responds to the fourth suit with a jump bid it shows 15+ points but no stops in the fourth suit. This is game forcing.
The convention does not apply if:
● Responder has passed
● There is an overcall or takeout double
● The bidding is all at level one (1C, 1D, 1H, 1S)
● The fourth suit is bid in the third round
● The opener jump bids her second suit
● The opener reverses