Responder Promises a FIVE Card Suit

Normally when Responder bids a new suit they only promise a FOUR card suit. Example:
This is the auction:

Opener	Responder
1♥	1♠

Responder is showing at least four ♠ and at least 6 HCP (High Card Points).

(Remember their PARTNER opened the bidding. OPENER needs FIVE ♥ and 13 HCP to open the bidding but Responder only needs 6 HCP and a FOUR card suit to respond.)

How about another auction?

Opener	Responder
1♣	1♥

Responder is showing at least four ♥ and at least 6 HCP (High Card Points). Responder could have more than four ♥ but they do not promise more than four ♥.

What happens if Responder responds at the 2 level? Does that change things?

No.

Take this auction:

Opener	Responder
1♥	2♣

Since Responder bid a new suit at the 2 level they show at least 10 HCP BUT they are still only showing four ♣. They could have more. (They might even have less if they are stuck!)

HOWEVER there is ONE auction where Opener opens a suit at the 1 level and Responder bids a new suit without jumping and they promise FIVE in the suit.

Do you know the auction?

Opener	Responder
1♠	2♥

This is the ONE auction where Responder promises a FIVE card suit. When Opener opens 1♠ (they MUST open 1♠) and Responder bids 2♥ (again they MUST respond 2♥) this shows that Responder not only has the 10 HCP required to bid at the 2 level but also has a FIVE card ♥ suit.

WHY? Why would the inventors of this bidding system do that to us? Why make us memorize one more thing?

The reason is simple.

It is INCREDIBLY easy to find a FOUR FOUR ♥ fit once Opener opens the bidding 1♠. However if you allow that Responder could have only a four card ♥ when the bid 2♥ then it would be impossible to find a FIVE THREE ♥ fit when Opener opens 1♠.

Don't believe me? I don't blame you. Let's see this in action.

Here is your hand:
♠Q3
♥AK93
♦KJ72
♣874

Partner opens the bidding 1♠. Here you might want to bid 2♥. This violates the four card suits up the line rule but you do it at the 1 level so why not the 2 level right? So you bid 2♥.

Opener has:
♠AK762
♥J852
♦Q3
♣A2
Opener raises your ♥ suit to 3♥ since they have a fit with minimum values.

You bid 4♥ triumphantly! "See, we NEEDED to bid 2♥ in order to find our fit!" you cry.

Hmmmmm. Really?

Let's take your hand. Partner opens 1♠ and you have this hand:
♠Q3
♥AK93
♦KJ72
♣874

Let's say that instead of responding 2♥ you respond 2♦. (Four card suits up the line.) Do you lose that ♥ fit?

NO!

Over 2♦ guess what Opener is going to bid?

Opener has:
♠AK762
♥J852
♦Q3
♣A2

2♥. Now you have found your ♥ fit. You can bid 4♥ and you will have made it to your game in ♥.

Well, what does it really matter?

Here's where it matters.

When Responder has this hand:
♠Q3
♥AK963
♦KJ7
♣874

and Opener has:
♠AK762
♥J85
♦Q63
♣A2

and Opener opens the bidding 1♠.

If Responder promises FIVE ♥ when they respond 2♥ then the partnership will have found their five three ♥ fit and be safe and happy in 4♥. Responder will bid 2♥. Opener will know they have a FIVE card suit and can raise with three. Opener will bid 3♥ and Responder will bid 4♥ to get the partnership to game.

But what happens if Responder only promises a FOUR card suit. Now over 2♥ Opener cannot show a fit. They will probably bid 2NT to show a minimum, balanced hand.

What does Responder do now?

If Responder bids the ♥ again they show a SIX card suit. (On most auctions when Responder rebids their suit they show six cards in that suit.) But Responder does not have a six card suit.

Responder would probably just bid 3NT and hope for the best.

With an eight card fit, playing in four of a major tends to be better for playing in 3NT. Especially when you are a newer player.

Imagine what will happen if the Opponents lead a ♣? Would you rather bid in 3NT or 4♥?