The Macaw 1 Diamond
We have restricted all our opening bids at the 1-level by points and/or shape. A major suit must have 5 or more cards to open at the 1 level. Balanced hands with 15-17 HCP should be opened as 1NT. Additionally in Modern, we open all balanced hands with 12-14 HCP as 1♣. That includes hands with equal or longer diamonds than clubs.
That leaves remaining hand patterns to be opened as 1♦. You see that opening strength hands without a 5 card major and are not balanced (nor have a long club suit when unbalanced) will be unbalanced with at least 4 diamonds. I could run through the math, but try generate a few examples on your own. The only hand pattern that doesn't meet the requirements is the dreaded 4-4-1-4 shape hand - with a singleton diamond.
So, when we open 1♦ we promise that we have 4 or more diamonds AND a shortness (singleton or void) in another suit. If we don't have any shortness, then we promise 6+ diamonds. Note, a hand with 5 ♦s and NO shortness is not going to open 1♦. It will open 1NT (if strong enough) or 1♣. See the Toucan Club details for reasons why we find it better to open 1♣, with any balanced hand with 12-14 HCP. Because of these promises/agreements as to what open 1♦ means in our system 1♦ needs to be alerted. In fact, the modern minors system should be pre-alerted at each table.
Alert: we play a transfer club system, opening 1♣ could be as few as 2 and could have longer diamonds. We make transfer responses to the 1♣ bid
Alert: 1♦ promises 4+ card diamond suit AND unspecified shortness. If they don't have shortness, they will have 6+ card diamond suit
This promise of an unbalanced hand is extremely useful in the auction to communicate both shape and opening hand strength. Responses by the responder are natural, show their first best suit at the 1-level, raise (inverted) diamonds with support. Responder should have some trepidation about responding in No Trump; understanding that opener has a singleton of void somewhere.
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