PhilKing, on 2013-January-15, 11:35, said:
It's fairly common if playing five-card majors with a 2+ club to play play double after 1
♣-(1
♥) to try and locate a minor suit fit (and denying four spades) - a posh version of "stolen bid" double, if you like. After a natural diamond, that is less important, so we may as well distinguish between four and five spades.
I can't remember the second reason.
After a 2+ 1
♣ opening, it can clearly workd out badly to raise to 2
♣ with "only" 4-card support, so it can be handy to us double to show a hand with values but no convenient bid.
After a natural 1
♦ (or natural 1
♣) opening, opener can just raise the minor with 4-card support, and on (depending on style) some hands with 3-card support also. Thus Responder can normally find something to bid, so the "values but no convenient bid" hands are a lot less frequent.
Maybe that's the second reason, or maybe I'm just expressing the first reason in a different way.
PhilKing, on 2013-January-15, 16:26, said:
After One Club we just play 1
♠ as fewer than 4
♠, 1NT as nat and 2
♣ as diamonds and 2
♦ as clubs. After One Diamond it's mostly the same except 2
♦ is limited, often with three-card support. As you probably recall, after 1
♦-1
♥, 2
♥ is a transfer to 6NT down 6 when partner forgets it shows spades.
This misunderstanding must be quite common. It happened against me a couple of months ago and the opponents ended up in 6NT-8! I never found out what the actual agreement was, but there's does seem to be an obvious advantage to natural methods.