Blackwood
Initiate Blackwood by a bid of 4NT. This is asking a direct question of partner: "How many aces have you got?" and as such is forcing.
The response is coded:
| Response | Number of aces |
|---|---|
| 5C | 0 or 4 |
| 5D | 1 |
| 5H | 2 |
| 5S | 3 |
This might be enough information, or you might find in some cases that you want to know about kings as well. In which case, a bid of 5NT by the initiator asks the same question but of kings, with responses at the 6 level; it's generally considered a car-parking offence to king-ask unless you hold all four aces between you.
The major criticism levelled against Blackwood is that the response levels are quite high. Particularly in a minor suit, simply bidding Blackwood might (depending on partner's answer) commit you to pass 5 of that suit and so you could be forced into a slam anyway. It's even worse if you ask for kings. Beware! (Because of this, some favour Gerber which is very similar but at a lower level.)
Escaping the convention
So you've bid Blackwood, had a not-very-good reply, and want to play in 5NT. How on earth do you do that without it sounding like you're asking for Kings?
The answer is to bid the unbid suit. This is a cue to partner to bid on...
Coping with interference
There are two ways to do this, make sure to agree in advance which you want to use.
- Use the D0P1 (Double = Zero, Pass = One) convention. In other words, double the interfering bid to show no aces, or pass it to show one.
- Treat the responses as starting at the next available bid (so e.g. over a 5D interference, 5H would show 0 or 4 aces, and so on). However this takes your bidding to a scary high place even quicker...
4NT that isn't Blackwood
4NT as a direct response to 1NT is usually invitational to slam as a balanced response; see under openings.