Asking bid

In contract bridge, an asking bid is a convention used to seek a slam accurately. There are two types - suit asking bids and notrump asking bids. Constructed by bridge pioneer Ely Culbertson in the 1940s, they have been superseded by other methods; however, one remaining commonly used asking bid is the 5NT Grand slam force.
The application of asking bids requires making distinctions between the asking suit, the agreed trump and the two remaining side suits. Replies by partner are in accordance with a schedule of defined meanings.

Definition

First there has to be an agreed trump suit. The trump agreement can be done explicit as well as implicit. Thereafter the first asking bid has to be either a double jump in a new suit not bid by the partner or the one who puts the asking bid forward, or at the fourth level. After an asking bid, the one who has put the first asking bid forward, will be like the Captain of a ship, and his partner has to reply to the questions. Only bids in the agreed trump can abort a series of asking bids.
Examples: After an opening of 1, partner's reply 3 establishes as trump. The bids 4, 4 and 4 are now asking bids. But also after a 1 opening, any double jump in a new suit is an asking bid, and agreed trump. After a 1 opening, 3, 4 and 4 are Asking bids. If 4 NT is bid before an asking bid has been put forward this will then be interpreted as Blackwood. But 4 NT is no longer a matter of the number of Aces, if 4NT follows after an asking bid.
The first asking bid is a question related to first and second controls. It is hence important to understand the definitions of the controls.
Defintition of first and second controls:

A first control equals a void or an Ace, with exception of trump, in which only the Ace counts as a first control, naturally.
A second control equals any singleton or a two card or longer suit with a Queen-guarded King. For instance King-Jack high isn't a sufficient second control, but King - Queen is a second control independent of the suit length. Also, a void can be both a first and a second control, but here the number of trump cards might be an issue.

Also third controls can be of importance.

A third control is usually about a doubleton, but can also be Queen guarded with a Jack and one card more. And possibly a void with many trumps on own hand. King-Queen in a doubleton with at least four trumps also is a third control. This is not the case with a third card in the suit.

What's the significance of an Asking Bid ?
The first asking bid, equals the following question - "Do you have the first control in this suit ? Or if not, do you have the second control in this suit and one first control in other suit ?"
Another asking bid, has exactly the same significance.
Example:
West opens 1, and East holds this hand:
1 - 3
4 - 4
5 - 5
6 - pass
But if repeating the first asking suit, then the second asking bid equals the following question - "Do you have the second control in this suit ? Or if not, do you have an even better control in this suit and one second control in other suit ?"
Example with the same hand :
1 - 3
4 - 4
5 - 5
pass
Further Asking bids
If the reply to the first asking bid allows 4 NT to be bid, a 4NT-bid then is asking for the number of Trump-top controls, the Ace, King and Queens of the agreed trump. And partner replies 5 = I have none of these three cards, 5 = 1 such card, 5 = 2, 5 = all three. If the bidding has passed 4 NT, this bid can instead be bid as 5 NT.. But if this has been possible to bid already, at one level lower, then will 5 NT instead ask for Trump-excess, or the number of trump cards that so far has not been possible to show.
An asking bid in another suit can also follow. Then it's called "a second asking bid". Asking in the same suit twice is called "a repeated asking bid" however. And this is different from a new asking bid.

Example and replies

Example:
Auction:
1 - pass - 3- pass
4 ? - pass - Reply in table below

Asking suit	Trump suit	Side suit	Reply	in this example
not even 2nd control	insignificant	insignificant	Trump, lowest	4
With second control in asking suit	-	-	-	-
2nd without any other 1st	not the Ace	no Ace/void	Trump, lowest	4
Constructive replies	-	-	-	-
2nd	Ace	no Ace/void	Trump jump	5
2nd	not the Ace	one void	void suit	4 / 4
2nd	not the Ace	one Ace	Ace suit	4 / 4
2nd	Ace	a void	side suit void	4 / 4
2nd	Ace	one Ace	4NT = 2 Aces, always	4 NT
2nd	not the Ace	one Ace + a void	suit of the Ace	4 / 4
2nd	not the Ace	both Aces	4NT = 2 Aces, always	4 NT
2nd	Ace	one Ace + a void	4NT = 2 Aces, always	4 NT
2nd	Ace	both Aces	5NT = at least 3 Aces, always	5 NT
With first control in asking suit	-	-	-	-
void	not the Ace	no Ace	raise asking suit	5
void	not the Ace	one Ace	side suit Ace	4 / 4
void	Ace	no Ace	Trump jump	5
void	Ace	one Ace	4NT = 2 Aces, always	4 NT
void	not the Ace	both Aces	4NT = 2 Aces, always	4 NT
void	Ace	both Aces	5NT = at least 3 Aces, always	5 NT
Ace	not the Ace	no Ace/void	raise asking suit	5
Ace	not the Ace	one Ace	4NT = 2 Aces, always	4 NT
Ace	not the Ace	a void	side suit void	4 / 4
Ace	not the Ace	one Ace + void	4NT = 2 Aces, always	4 NT
Ace	not the Ace	both Aces	5NT = at least 3 Aces, always	5 NT
Ace	Ace	no Ace/void	4NT = 2 Aces, always	4 NT
Ace	Ace	a void	4NT = 2 Aces, always	4 NT
Ace	Ace	one Ace	5NT = at least 3 Aces, always	5 NT
Ace	Ace	one Ace + void	5NT = at least 3 Aces, always	5 NT
Ace	Ace	both Aces	5NT = at least 3 Aces, always	5 NT

Hands with two voids are not taken in consideration. Presumably not by Culbertson, certainly not in the source.
The basic principles are -

Without even the second control in the asking suit, reply negatively - logically trump at lowest level. This applies completely to the situation in the trump and side colors.
Also with a second control in the asking suit, but no other first control, reply negatively - logically trump at lowest level.
If the requirements of either a first control in the asking suit - or at least a second control in the asking suit combined with one or more first controls in Trump and the side suits are met, then reply constructively.

The constructive replies:

With just one first control, this should be shown. Question suit raise, trump raise or a bid in the side suits.
With more than one first control, the side suits comes first. Unless there totally are two Aces on the replier's hand.
4 NT always means exactly two Aces
5 NT always means at least three Aces

Tactics
When a slam seems possible, and especially when this depends on partner's controls in a certain suit, then asking bids may well be the road to follow. If asking in a suit in which you have either the Ace or the King, you may get splendid excess information.

Applicability

Asking bids, although developed for the Culbertson bidding system, which today largely has become obsolete, can be used in combination with most natural bidding system, such as Acol, Five Card Major and others. Like Blackwood and Cue bids, Asking bids are Slam-seeking.
It is indeed possible to use Asking bids together with Blackwood, even in one and the same deal. But Asking bids can never be used in combination with Cue bids, as they can't be distinguished from each other.
The advantages of Asking bids increase especially if used together with Culbertson's 4 and 5 NT conventions. Here the rules are very clear:
"If a series of questions begin with 4 NT, then that specific bid is Blackwood. But if the first question has been a bid in a new suit, then the 4 NT instead asks for the partner's trump top quality." The 4 NT bid is then asking for the number of top three trumps, then a later 5 NT bid, asks for additional trump length. Whilst a 5 NT bid not preceded by any 4 NT bid, equals the Grand slam force convention.
After a first Asking bid, then the 4 NT bid asks for "trump top quality".. If 4 NT is followed by 5 NT, then that bid asks for "trump length". Here the replies are based on what's the minimum number of cards for a usual trump agreement length. Replies - 6 = no extra trump card; 6 = one more; 6 = two more.
When preceded by the "non-Blackwood" 4 NT trump top quality bid, any thereafter following 5 NT bid must be understood as "Any additional, not yet shown trump cards ?", which isn't equal to the 5 NT Grand slam force.
If using Asking bids, the player who first put an Asking bid forward, must thereafter be "the Captain" of the couple for the remaining part of the auction. The partner has to rather take on the role of a private soldier, and stick to giving correct answers to what very well may become a series of questions. This isn't limited to always be the opener, but is often the case. Cue bids are from that perspective different.
And it has to be added that Cue bids today more or less has put the Asking bids to history. But Culbertson's 5 NT Grand slam force is still in use.