Conventions in depth
An opening of 2♦, 2♥ or 2♠ that shows a good six-card suit and about 5 to 10 points.
The opening is a pre-empt, made on less than an opening bid to use up the opponents’ bidding room. (2♣ is not available for this: it is reserved for the strongest hands.)
Because partner will often raise, the suit needs some quality, and more when vulnerable:
BidMaestro also holds back from a weak two when the hand contains an outside four-card major, except in third seat, where the pre-empt is freer. That extra major is worth too much to bury under a weak bid.
Opener has already limited the hand tightly, so responder is the captain:
In fourth seat there is no weak two. With three passes in front of you a hand this weak passes the deal out, and a two-level opening of 2♥ or 2♠ is constructive instead: a six-card major with about 12–15 points.
A weak two takes away the one- and two-level room the opponents need to find their fit, on a hand too weak to open otherwise. The good suit is what keeps the pre-empt safe when partner has to raise.
