Conventions for Contested Auctions
In contested auctions a whole level of bidding space is taken away and you lose the ability to differentiate between competitive/preemptive bids, constructive/invitational bids and game going bids. Many conventional bids have evolved to reduce the need to make your partner guess.
Partner has opened 1D, you have 7 points and 4 hearts, about to bid 1H, but pesky RHO bids 2C!!! Your side probably has the majority of the points. What now??
When playing the Negative Double, what if you want to double for penalties?
Partner opens 1H and you are about to raise to 3H with 10 points and 4 card support when RHO bids 2D. Now if you bid 3H partner will not know whether you are weak with 5 hearts (bidding to the level of your fit and not wanting partner to bid again), or whether you are still inviting game. How can you avoid making partner guess?
Partner opens 1H and you are about to raise to 3H with 4 card support and 4 hearts, when RHO doubles for takeout. Now if you bid 3H partner will not know whether you are weak with support and trying to silence LHO and don't want partner to bid again, or whether you are inviting to game. How can you avoid making partner guess?
Your LHO opens 1H and partner overcalls 1S. If you are weak with 4 spades you may want to make a pre-emptive jump to 3S and not wanting partner to bid on. But if you have 10-11 points and 3+ spades you may want to bid 3S inviting game if partner has 13+ HCP. How can you avoid making partner guess?
Partner opens 1NT. You have a game going hand with hearts and are planning to bid Stayman or Transfers when RHO overcalls 2S. (LHO must be very weak). You have game somewhere, but how can you find it? How can you let partner know that you are not just competing for the part score?