[PhilG007]

When is the bid 4NT Blackwood and when is it not? I ask this question for the benefit of the novices and intermediates who
read theses forums. It's an age old question and it still causes confusion and heated post mortems.

[Stephen Tu]

To a certain extent it is up to partnership agreement. But in general better players play it is not blackwood more often than novices/int who are more apt to always play it as blackwood. Generally Blackwood applies after suit agreement, natural quant applies if partner's bid previous bid was natural NT, or if no suit has been agreed yet.
These agreements should mostly be assumed, IMO:Not blackwood:

• Over partner's natural 1nt/2nt bid/rebid. E.g. 1nt-4nt, 2nt-4nt, 2c-2d-2nt-4nt, 1c-1s-1nt-4nt, 1c-1h-2nt-4nt
• Raising partner's natural 3nt offer to play bid. Except if the 4nt bidder's previous auction has been to show a strong one suited hand, e.g. something like 1c-1s-1nt-3s-3nt-4nt, if 3S is strong GF one suited. Or similar like 1c-2s(strong)-2nt-3S-3nt-4nt.
• If your previous call was stayman. 1nt-2c-2s-4nt = invite to 6 no spade fit (presumably you had hearts). If you want to blackwood agreeing spades, play a Baze variant (4c = kc ask, or 4d = kc ask), or use 3OM (1nt-2c-2s-3H) to set trumps first if not playing Baze.
• If your previous call was Jacoby transfer. 1nt-2h-2s-4nt = invite with 5 spades. If you want to set spades as trumps and keycard, texas xfer instead. 1nt-4h!-4s-4nt = kc.

In general if you want to blackwood set trumps first if at all possible. If your 3nt is to play you almost always want some sort of 4nt = I'm a bit too strong for 3nt.

[ahydra]

Stephen's answer covers the constructive bidding situations*, but perhaps the most common situation is probably competitive bidding, where it normally shows two places to play rather than Blackwood. Some examples:

(1S)-4NT: pre-empt both minors
(1S)-X-(4S)-4NT, (4S)-4NT, (4S)-X-(p)-4NT, and the like: two places to play. Partner assumes you have minors, and if you in fact have hearts and a minor, you correct the wrong minor to the next suit up that you do actually have.
1S-(3H)-p/X-(4H); 4NT = strong, 3-suited takeout, very shapely so not suitable for X in case it is left in (as will often happen). For example KQJ10x - AKxx KJxx. Note that if responder had instead bid a suit or supported spades then 4NT would be RKC for that suit

Of course, opening 4NT is normally defined as specific ace ask (or a pre-empt with both minors).

Also of note is that a common agreement is to play a direct 4NT response as regular Blackwood rather than RKC. 1D-(1H)-4NT, for example. Responder probably has a weird shapely hand and just wants to get to the right level of slam in his suit.

* I would also add 4SF default rebid situations like 1D-1H; 2C-2S*; 3D (no S stop, no 3H)-4NT = not RKC for diamonds, but natural and quantitative.

ahydra

[spotlight7]

ahydra, on 2019-November-26, 17:24, said:

Stephen's answer covers the constructive bidding situations*, but perhaps the most common situation is probably competitive bidding, where it normally shows two places to play rather than Blackwood. Some examples:

(1S)-4NT: pre-empt both minors
(1S)-X-(4S)-4NT, (4S)-4NT, (4S)-X-(p)-4NT, and the like: two places to play. Partner assumes you have minors, and if you in fact have hearts and a minor, you correct the wrong minor to the next suit up that you do actually have.
1S-(3H)-p/X-(4H); 4NT = strong, 3-suited takeout, very shapely so not suitable for X in case it is left in (as will often happen). For example KQJ10x - AKxx KJxx. Note that if responder had instead bid a suit or supported spades then 4NT would be RKC for that suit

Of course, opening 4NT is normally defined as specific ace ask (or a pre-empt with both minors).

Also of note is that a common agreement is to play a direct 4NT response as regular Blackwood rather than RKC. 1D-(1H)-4NT, for example. Responder probably has a weird shapely hand and just wants to get to the right level of slam in his suit.

* I would also add 4SF default rebid situations like 1D-1H; 2C-2S*; 3D (no S stop, no 3H)-4NT = not RKC for diamonds, but natural and quantitative.

ahydra

4NT is a natural sign off when partner suggests slam in a minor and your hand does not offer slam chances.

1S-2H-3D-3N-4D-4NT

[Winstonm]

PhilG007, on 2019-November-26, 14:29, said:

When is the bid 4NT Blackwood and when is it not? I ask this question for the benefit of the novices and intermediates who
read theses forums. It's an age old question and it still causes confusion and heated post mortems.

I think this is a great question for any partnership, so much so that even the great Italian Blue team had rules for just this situation: their rule was that it is only ace-asking if the bid came in the first two rounds of bidding or if there was a jump to 4NT. (other than a quantitative NT raise, of course)

[pescetom]

Interesting discussion, maybe it should be under Intermediate/Advanced.

ahydra, on 2019-November-26, 17:24, said:

Also of note is that a common agreement is to play a direct 4NT response as regular Blackwood rather than RKC. 1D-(1H)-4NT, for example. Responder probably has a weird shapely hand and just wants to get to the right level of slam in his suit.

I would state the agreement here as "Blackwood is regular rather than RKC unless trumps have been fixed or imposed, or we are under duress" - probably saying the same thing.

Another tricky area is 4NT once a control-bid has already been made. A typical intermediate agreement is that 4NT is always RKC even after one or more control-bids have been exchanged, but more advanced pairs playing indifferentiated control-bids will have strict rules about when (if at all) 4NT is RKC rather than Turbo or responsive. I like to play that it is RKC only by a player who has not yet made a control-bid (in other words played in response to the first control-bid).

And another one that needs partnership agreement is the meaning of 4NT when trumps are fixed and we have a lower Kickback available.

[barmar]

pescetom, on 2019-November-27, 10:46, said:

I would state the agreement here as "Blackwood is regular rather than RKC unless trumps have been fixed or imposed, or we are under duress" - probably saying the same thing.

While that's "expert standard", I wouldn't depend on a random understanding it without discussion. If you're playing with a pickup partner and it goes 1♠-4NT, it's more likely to be RKC than regular BW.