Cool, one of the first things one learns in beginning bridge days is that there is this neat convention where 4N “asks for aces”. Pretty nifty!! That way you can figure out whether you can take 12/13 tricks or less than that.
However, the plot thickens quickly when someone informs you that over nt, this bid is meant as “quantitative”. Quantitative means it's an inquiry about how much you have in overall values, as opposed to an inquiry about something specific, like number of key cards. So, confusion often arises as to when a 4N bid is “quantitative" or “ace asking”.
Here’s my slant on the subject.
When opener denotes a balanced hand that has a range, we use 4N as an asking bid for slam, thus quantitative. There are lots of auctions where opener denotes a balanced NT hand of some sort with specific ranges:
1N (15-17) usually
1C 1D, 1N (12-14) usually
2N (20-21) usually
2C 2D, 2N (22-24) usually
4N over these types of auctions asks opener to accept a slam invite with a max or pass the invite for a 4N contract.
The auction after a quantitative bid are not relegatedto NT contracts, however. Often folks will play them “Baron” style which means one will accept the slam invitation by bidding a four card minor at the five level. The hand may fit better in a 4/4 minor fit for 12 tricks rather than NT. Thus: 1N 4N, 5C.
One can also accept the slam invitation by bidding six of a minor. This denotes a five card suit or better and request responder to agree to the minor suit slam, or correct back to NT. Thus 1N 4N, 6C.
In order to ask for aces, we use 4C Gerber replacing the traditional 4N bid. This serves the purpose of keeping many nt auctions lower and the ability to bail at 4N when that seems right.
Quantitative bids are also often used in minor suit auctions once the contract has settled in 3N. Now 4N is a “slam ask” for strength.
1S 2C, 3C 3N, 4N.
Since it’s usually wrong to take 3N out to 4m, 4m in this auction now says “I’m interested in slam, but not NT yet. Please start Q bidding if you accept, bid 4N sign off if you don’t. In these type auctions, 4N is showing as much as asking--i.e., it says "I have substantially more than I have shown from my prior actions, but not enough to drive to slam, so act accordingly
In order to divine whether 4N is ace asking or quantitative one might ask what a 4m bid would mean at the same point of the auction. If this bid is ace asking or a suggestion to start Q bidding, then 4N is probably quantitative. That is a round about way of going at it, but it might help to think that way when you’re dead tired in the finals of the Spingold and about 100 different notions are taxing your brain –mostly how to win the thing!