4th Suit Forcing is an artificial game-forcing bid by responsder (on the fourth bid) of the partnership’s previously unbid fourth suit (i.e the first 3 bids were all of different suits). It does not necessarily show or deny the actual suit bid.

Example

North East South West
1♦ - 1♠ -
2♣ - 2♥1  

1artificial, 12+ points. May or may not have ♥s.

System is off:

  • 1♣-1♦-1♥-1♠. (1♠ is natural here.)
    1♣-1♦-1♥-2♠ is 4th suit forcing, 2♠ being artificial.
    This keeps the posibility of finding a ♠ match at a low level while still keeping plenty of space above the game-forcing bid.
  • after opener’s reverse. Any bid other than blackout is game-forcing so 4th suit forcing is redundant.
  • after opener’s jump shift.
  • in competition.