'The most interesting questions from visitors to the Dutch sister site (Bridgevaria.nl)'. 

Dear Ed & Peter,

Does my 1♠ bid below show at least four or at least five spades?

Thanks,
Len de Jonge

 Answer Ed Hoogenkamp (South)

Dear Len,

This is a systemic matter. The answer depends on whether you as a responder play a negative double directly over the opponent's 1♥ overcall.
If you do not, your bid shows four or more spades.
But if you do play a negative double here, this is by far the most popular agreement:

¹ Precisely four spades

¹ At least five spades

You can distinguish between four and five or more spades, since the negative double shows a spade suit.

In Norway negative double (nægåtif døbbel?) means you have a bust — I think. So perhaps this influences the meaning of 1♠. Peter knows all about it.

Un saludo, greetings from Barcelona

Answer Peter van der Linden (North)

Dear Len,

First I have to correct Ed, nothing new here. In Norway a 'negativ dobling' means exactly the same as it does anywhere else (except perhaps in the lesser areas of Barcelona).
It's no big deal Ed's Norwegian is poor (so is my Spanish). A problem is though, that his historical understanding leaves a lot to be desired for. He thinks, for instance, that the Spaniards won the battle of Nieuwpoort (Nuevoporta? Nieuport? Newport?) — remember the year, Ed?
(For non-Dutch readers: this battle was fought in 1600, during the Dutch war of independence against Spain; 'the eighty years war';1568-1648. The Dutch under commander Maurits (Maurice) of Orange, from the house of Orange — the current Dutch royal family is still from this house — defeated the Spanish. It is one of the years every Dutch school kid easily remembers since it is such a round number. In Dutch bridge parlance a four number win or loss is called a 'jaartal' (year). The year of the battle is of course a well known bridge score...)    
I mention 'historical understanding' since in order to understand the how and why of the negative double, it helps to have some understanding of its history.
Originally the Sputnik double (as the invention of Americans Roth-Stone became known in 1957, after the first Soviet space satellite was launched into orbit in that year) was used in this situation:

¹ Four hearts (more are possible but only if South has fewer than 10 HCP)

So the archetypical negative double meant: 'I wanted to make a bid that has been made impossible by the opponent's overcall'

Quickly players began to use it in other situations as well:

¹ Four diamonds?!

Not very practical, so it turned out. In bidding the major suits should always have priority. Though South could have bid 1♠ — East's overcall hasn't made it impossible — players chose the meaning Ed mentioned earlier: precisely four spades. A 1♠ bid by South would show five or more spades.
So in this case we take advantage of their overcall in order to give partner more information!
Anyway: so far a negative double shows only a major suit.

Now what if both majors have been bid?

¹ Both minors

Note that here too East's overcall hasn't made any bid of South impossible. So here too we take advantage of their overcall.

¹ Both minors

In this case the overcall did cut short South's possible 2♣/♦ bids, so this is a classical negative double (by the way: it is by no means a rule that this double must be negative; a penalty double is certainly a possibility).

And about that battle of Nieuwpoort/Nuevoporta: Ed, I'll tell you once again: Prince 'Mauricio' doubled the Spanish there... for penalties! The fact that your fellow-countrymen redoubled was not very clever, to put it mildly, since that turned the score into a year: down three redoubled and vulnerable.

En hils, regards from Orkanger