[maris oren]

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North opens 1♠. East passes. Using 2 over1 system what should South bid? 2 ♦? Are 4 cards enough?

[smerriman]

4 cards in a minor are plenty. If the hearts and diamonds were flipped it would be a slightly trickier decision; then it's a case of deciding the best lie (or having 2♣ being more artificial).

[awm]

South only has twelve cards. If the 13th card is a spade, 2nt Jacoby is clear. If it’s a diamond then 2♦ is obvious.

Otherwise the standard is to bid 2♦ on four, but there’s a trend to prefer 2♣ on this hand type by many players so that bid becomes “clubs or balanced” and the 2♦ bid can promise five. Partnership agreement of course.

[Cyberyeti]

How many cards ? 13 would be a good start, 3342 is not a full hand.

3442 2♦ is fine, 3343 some people play 3N as 33(43) 13-15 otherwise 2♣/2♦ to taste

[pescetom]

BWS, many experts, and even me play that 2♦ should be 5-card and thus South (with another ♣/♥/♠) should reply 2♣ here.
But Larry Cohen and others would cheerfully play 2♦.
The most important thing is that you are both singing off the same sheet.

[fromageGB]

If you are playing forcing NT, then if you have no 2♣ agreement, an option is 1NT here, keeping 2♦ for 5 cards. One of the advantages is that knowing of a decent 5 card suit opposite can make a difference to a strong opener looking for slam.

If you want to put non-natural options into 2♣, a good idea is to have 2♦ as an almost obligatory relay followed by responder clarifying his hand. This could be :
2♥ = 16+ and 4 hearts (<16 starts 1NT)
2♠ = 11/12 3 card support NF. This is the only non-GF option and can be passed, so is safer than having to go 3.
2NT = 16+ 2344 or perhaps a lousy 5 card minor (<16 starts 1NT)
3♣ = natural 2/1, 13+, 5+clubs
3♠ = 13+ 3 card support. After which you use your standard non-serious/cues/etc.

[sfi]

awm, on 2020-June-09, 15:31, said:

South only has twelve cards. If the 13th card is a spade, 2nt Jacoby is clear. If it’s a diamond then 2♦ is obvious.

With one partner, the 13th card results in four different actions!

• Spade: 2NT FG raise
  
• Heart: 2C FG clubs, FG bal or INV raise
  
• Diamond: 2D 5+ suit FG
  
• Club: 3NT balanced 3-card raise

[paulg]

Another reason why many play that 2♣ can be natural or balanced is that you are not forced to introduce a poor suit into a 2/1 auction.

For example, even the '2♦ promises five' advocates would be nervous of bidding it with something like:

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The downside is that you lose the ability to show values in clubs but I believe the value of maintaining integrity in the other suits is a worthwhile sacrifice.

With the actual hand I don't mind 2♦ with such a concentration of values. Partner will likely evaluate correct most diamond holdings opposite.

But it is a tricky area of 2/1 that a partnership needs to discuss.

[Chas_P]

Since the question was "are four cards enough" I assume the missing card in the diagram was a club, so 3343 shape. Here's what my partner and I do with hands like that: Responder bids 1NT forcing, then no matter what opener bids next responder bids 3NT. This bid says, "Partner, we have a game but my hand is 4333 shape with one of the 3s being in your major. So we have an 8-card fit, but my hand has no ruffing value. You decide whether you want to play for 9 tricks or 10."