Modern competitive bidding is, to a large degree, about avoiding the last guess. It is the title of the very first subchapter in Robson & Segal, and with good reason. In a competitive auction we want to combine applying maximum pressure, to put our opponents to a guess, with descriptive bidding so we will not be the ones guessing.
On this auction North has kindly granted you some extra rounds of bidding space by bidding low. As mentioned by smerriman, and greatly supported, West should make use of that space. On hearing the 3
♠ bid West's thoughts should be as follows:
- I know I am always bidding game. I have an extra heart and extra playing strength, and even though partner can be quite weak for the 3♥ bid under pressure, it pays to bid vulnerable games.
- The opponents are not vulnerable, have a spade fit, and I have a singleton. They might bid 4♠ over my 4♥, though it is surprising to take four bids to get there when I am planning on bidding a game to make. Usually weak hands bid more quickly.
- If they do bid 4♠, I am not sure what to do. A case could be made for pass, double and 5♥. Some partnerships also play forcing passes on some of these auctions, and I should think about setting one up or not for our side. Is it costly to lose the ability to defend 4♠ undoubled? And how do I best involve partner?
So far it's mostly a recap of what others have already pointed out. My own minor contribution here is that I think that it is somewhat fine to say that the question as posed
has no good answer. Of course some particular action is the highest expected value conditional on freezing the auction up to West's third bid - something must always be best on average. But this exact problem is so pervasive and difficult to solve that we make entire lists of agreements to avoid it. Any decision in passout seat over their 4
♠ is very committal. My position is that we simply do not have the information required to get this right reliably, or even a good amount of the time. And the reason we do not have enough information is that we failed to listen to the auction on the past two-and-a-half rounds of the bidding, and did not make use of alternatives when we had the chance.
There are many ways to play changes of suit in competition, though my personal experience is that most people will have no agreements about them. In the style I prefer 4
♣ does not need to be slammish (though this is also not ruled out), does not guarantee the balance of strength, is not lead directing (especially not since partner won't be on lead. But even if that might be the case, it is not lead directing), does not set up a forcing pass and does ask partner to evaluate the prospective double fit and bid 5-over-4 with club support.
As East I would definitely bid on over 4
♠ on hearing 4
♣. We have four card support in clubs, an extra trump, an outside ace is always good, and a maximum for our previous bid. Our spades are also encouraging - on the auction it seems likely that North-South have 10 spades (even though this time they only have 9), meaning West has a void. Having zero spades wastage is a plus, or, being slightly more precise, the lack of values in the opponents' trump suit activates the '30 point deck' argument and also should lead us to decrease our estimate of our defensive prospects. All signs are green, it's time to go go go! Bid one more.