Blackwood has always been one of the most important tools for bidding slams and grand slams. Another way of looking at it - it is a tool for keeping you out of slam or grand slam!
The key idea: Don't go to slam missing two aces - that will typically mean 1 off.
How it works: Traditionally the bid of 4NT said "How many aces do you have". Partner would respond 5♣ with none, 5♦ with 1, 5♥ with 2, 5♠ with 3, 5NT with 4.
Blackwood is simple and still has its place in modern bridge, there are certain auctions where experts have agreed that 4NT is still the traditional Ace ask, for example often 1♠ 4NT - an immediate 4NT there is often simply Ace ask, responder may have a hand like this ♠5 ♥AKQJ1043 ♦K2 ♣AKQ, and just wants to ask about Aces.
Roman Key Card Blackwood (RKCB)
This has become the almost standard tool that intermediate or better partnerships are using. It has replaced the traditional Ace ask with a tool that asks for Aces, the King of trumps and the Queen of trumps. It asks for Keycards, there are 5 keycards - four aces and the king of trumps.
On this hand south opened 1♠, partner bid 2NT Jacoby which shows 4+ card spade support and is game forcing. The subsequent 4NT is RKCB with spades agreed.
NB: One thing that is subject to agreement, decide with partner whether you are playing 14/30 or 30/14. Let's assume we play 14/30 and see how it works.
Responses to 4NT:
- 5♣ - 1 or 4 keycards (so because we are playing 14/30, 5♣ shows 1 or 4. If you were playing the other way around, 5♣ would show 0 or 3 - discuss with partner which you are playing).
- 5♦ - 0 or 3 keycards
- 5♥ - 2 without the queen of trumps
- 5♠ - 2 with the queen of trumps
What you may notice is that 5♣ and 5♦ responses do not specify whether the player has the queen of trumps. There is a way to still ask about that though, the player just bids the next highest suit (not including the trump suit - If the key card bidder bids the trump suit at the 5 level it is sign off).
So, let's continue and also look at how to ask for the Queen of trumps in that auction,
Here we have shown 1 or 4 keycards, (partner will know it's 1 - we showed a weak hand over 2NT, and also he is probably looking at 3 or 4 of them!). Now partner has bid the next highest suit, 5♦. This says - do you have the Queen?
We respond as follows
If we do NOT have the queen, we simply sign off, by bidding 5♠.
If we do have the queen, we do NOT sign off. We either bid 5NT, or, even better, bid your lowest King. So, over 5♦, we could bid 5♥ which says: I am not signing off because I do indeed have the Queen (without it I would sign off to show you), and I am also bidding my nearest King, which is in hearts.
That is hopefully a good introduction that will cover almost all of your auctions. I will do a further article to look at a few more details and finer points. Including further follow ups, what auctions are RKCB and what might be "quantitative 4NT", as well as other issues