LEARNING CENTER

Game forcing raise with four hearts. This is the very popular convention Jacoby 2NT. If you alert partner's 2NT and someone asks what it means, though, you shouldn't say "Jacoby", but rather "Game forcing raise with four hearts."

This is a strong bid and while you don't need a full 13 HCP, you should have some real values in addition to any extra points you count for shape. 

Note: some advanced players use a tool called "Modified Jacoby 2NT" which is slightly different and requires study. 

Clubs and Hearts. While some players always use 2NT for the minors on this type of auction, it's less likely that you will have the suit the opponents opened than the other two suits. Your strength depends on vulnerability, but this is always at least 5-5 in the two suits shown. 

18-19 Balanced. Wow, that's a laundry list of possible meanings, and it's why you need to have agreements with partner. The old fashioned way to play is 8-9 balanced, but many players use 4-way transfers. If you do play 4-way transfers (and 3 shows that you like diamonds), then you can use 2NT with both minors to play in 3 if partner likes diamonds or 3 if partner doesn't like diamonds. 

Other. This bid does not exist. South does not want to "steal" playing notrump from the 2 opener. 2, waiting, is still forcing and South can show values later. 

18-20, balanced, with hearts stopped. South can not preempt in balancing seat and so this can't be a weak bid. The reason you need a bid to show 18-20 is that a balancing notrump is about 11-14. Doubling and bidding 1NT is 15-17. So you can jump to 2NT to show 18-20 (the next range we need). 

Other. This bid does not exist. Responder has fewer than 5 or 6 points. That means that 2NT could be a lot of trouble if responder has the 0 points promised. Opener can still show 18-19 with a stopper by rebidding 1NT; with <15 balanced, he would simply pass.