Opening 1 Diamond

Refresh yourselves on opening the bidding 1 of a minor by reading this post:
Opening the Bidding

When you open the bidding 1 of a minor you only promise a THREE card suit.

That makes sense.

With three ♣ AND three ♦ ALWAYS open the bidding 1♣. No matter how bad your ♣ suit is and/or how good your ♦ suit is. So with the following hands open the bidding 1♣:

Hand A	Hand B	Hand C	Hand D
♠Q62 ♥K873 ♦AKQ ♣854	♠A632 ♥K83 ♦AQ4 ♣964	♠AK83 ♥KJ3 ♦AK4 ♣542	♠AQ3 ♥K832 ♦KQ8 ♣432

This makes less sense. Why would I want to do that? Wouldn't I like to tell Partner about my nicer minor?

No.

The reason we do this is this gives us a quick way of letting Partner know we have FOUR ♦ in our hand when we open 1♦.

I know what you are thinking. So this means when I open 1♦ I show a FOUR card suit?

No, you just show a THREE card suit. BUT if you always open 1♣ with three ♣ and three ♦ then the ONLY time you open 1♦ is when you have two four card majors. Therefore if Partner responds 1 of a major to your opening 1♦ bid and you DON'T support them you MUST have FOUR ♦.

Let's see this in action:

Hand A:
♠AQ62
♥94
♦Q983
♣AJ6

What will you open the bidding?

You have 13 HCP. You cannot open 1 of a major because you do not have a FIVE card suit. You open your LONGEST minor. Which is ♦.

So you open the bidding 1♦.

Now Partner says 1♥. What is your response?

Partner is showing at least 6 HCP and at least four ♥. You cannot support Partner. But you do have another four card major you can tell Partner about. Your response is 1♠.

This tells Partner you have four ♠ AND also tells Partner you have FOUR ♦. After all you do NOT have four ♥. You would have supported Partner if you did. Therefore you have four ♦.

Hmmmm. There MUST be a hand that does not have four ♥ and also does not have four ♦...

There isn't. Take away one of the ♦. Where do you put it? You still have to have thirteen cards! Can you put it with your ♠ suit?

No. Then you would have this hand:

♠AQ642
♥94
♦Q98
♣AJ6

and you would have opened the bidding 1♠ because you have FIVE of them.

What about this hand?

♠AQ62
♥942
♦Q98
♣AJ6

No. You have three ♦ and three ♣. You would have opened the bidding 1♣.

What about this hand?

♠AQ62
♥94
♦Q98
♣AJ63

No. You opened your LONGEST minor, remember? Here your ♣ are LONGER than your ♦ so you would have opened 1♣.

The ONLY hand you will open 1♦ with a THREE card suit is when you have a hand similar to this:

♠AQ62
♥K964
♦Q98
♣K3

This hand you must open the bidding 1♦. But now when Partner responds 1♥ you can support your Partner's ♥ suit and would rebid 2♥ to let Partner know you have a fit.

Does this work the same way with ♣? If I don't support my Partner's major after I open 1♣ do I promise four ♣?

No. The only reason it works with ♦ is because we choose to open 1♣ with three cards in both minors instead of 1♦.