[Antrax]

Playing against a suit contract, p leads a spot in an unbid suit in which you hold KJx(x). Dummy has no honor and plays low. You know partner would never underlead an ace (we don't go for being clever at this stage in our partnership), is it correct to play the J or the K? Does it matter which spot partner leads?

[aguahombre]

Not quite as basic as the question seems. Of course playing the Jack is a discovery play which cannot cost immediately. Either pard has led from the queen or she hasn't and you would like to know.

However, I can picture times when you know pard will be on lead next, not you. And it might be important for her to know the queen is a trick and that declarer did not start with AKT.

[1eyedjack]

Great little question.
Provided that you are absolutely certain that partner will not underlead an Ace (is there an ethical disclosure issue here?) then playing the J from this combination has a slight long term advantage. As the waterman says, there are circumstances in which ambiguity remains in the eyes of partner, but these are more than compensated by the play of the K denying the J.

But the advantage is I think tiny and only apparent at all provided that the partnership has an express agreement on the matter. I would be inclined to the play the K as standard from this holding
(1) to cater for the chance, however microscopic, that partner has just this once underled the ace, and
(2) to take away the need to think about it for those occasions when you play with another partner who is more inclined to do so, or in preparation for the day when your existing partnership relaxes this requirement however slightly.

[JLOGIC]

Depending on the hand, it could be right to play either the jack or the king, both for constructive and deceptive purposes. As a general rule play the king, because you never know if partner has chosen that hand to underlead his ace.

[nigel_k]

JLOGIC, on 2011-April-17, 13:06, said:

Depending on the hand, it could be right to play either the jack or the king, both for constructive and deceptive purposes. As a general rule play the king, because you never know if partner has chosen that hand to underlead his ace.

Agree. The assumption that partner will never underlead an ace is unrealistic and you have to cater for that possibility. Also, it depends a lot on who will be on lead next. Playing the jack could be very bad if partner will gain the lead, because he will think declarer has AK10 and give up on that suit and may also inferentially place you with other cards you don't have.

[FrancesHinden]

Either can work, but the king is normal.
If you are certain partner hasn't underled the ace, then what you might like to do is play the jack if you are going to gain the lead next, but play the king if partner is. But if you can work out who is going to be next on your side to win a trick, then you don't need to worry about this...

[Antrax]

nigel_k, on 2011-April-17, 14:32, said:

Agree. The assumption that partner will never underlead an ace is unrealistic

Why? I know you expert types sometime need to do such things when the situation calls for it, but neither I nor partner have found ourselves identifying such a situation yet. That's why I specifically requested to assume partner will never underlead an ace, since without that assumption the conclusion is obvious and not very useful to me at the table, where neither I nor partner underlead aces against a suit contract.

If declarer has the Q, it seems whatever I do leads to the same result: declarer wins, partner won't lead the suit again, declarer won't know where the other missing honor is.
If partner has the Q, then playing the K tells declarer where the Q and J are and partner will know his Q is good but won't know where the J is. Playing the J will tell declarer I have at least another top honor, and partner won't know that his Q is good.
So I guess I understand FrancesHinden's point. Thanks.

[vuroth]

It would be great if I was never dealt a hand with a lead problem, but as no expert, I've certainly underled an ace before, and will do so again.

[1eyedjack]

I think that the point made above that "you should not play the J because partner will place declarer with AKT" (my emphasis) is not really valid. Of course partner will with justification place declarer with AKT if systemically you have agreed to play the K from KJ and choose to depart from that agreement. But that is not what is being considered. What is being considered is that you systemically and by prior agreement play J from KJ and then subsequently play in accordance with that agreement. That being the case, AKT is one possible holding for declarer but not the only one. Partner may well be concerned that declarer might have that holding, but if he so assumes to the exclusion of other possibilities then he does so without justification.

Any agreement will give rise to some holdings that give rise to ambiguity. The suggested agreement only changes (contrasted with standard) on what holdings the ambiguity arises and is cancelled by the unambiguity of playing the King denying the Jack. Furthermore, there may be rare occasions when declarer (perhaps incorrectly) wins trick 1 with the king from an initial holding of AKT and removes from the perspective of the opening leader any ambiguity that would have been left in point had he played the ace.

The other points in the thread (whether to deceive declarer is more important than to assist partner etc etc, which defender is next likely to regain the lead, and whether partner may have as an aberration underled an ace) are all valid, but this particular point I think is not.

[Antrax]

vuroth, on 2011-April-18, 07:34, said:

It would be great if I was never dealt a hand with a lead problem, but as no expert, I've certainly underled an ace before, and will do so again.

Look, I'm honestly and truly sure there are great reasons to underlead aces, but we just never do it. That's why I'd like the answer to assume that's an impossibility, for the time being. We also don't play 2/1 GF even though I have no doubt it's a better system than the Standard American we're using now. I'm not saying it's great bridge, but it is the bridge we play right now. If the best solution to my third hand issue is to change the way we play, then these comments are relevant.

[1eyedjack]

I think that you are doing yourself down. If you have got to the stage where you can visualise the problem that you presented in the OP, you are not a million years away from occasionally underleading the odd ace.

One problem is that if you get into the habit of playing the J from KJ now, then when the time comes when you do (rarely) underlead an ace, your current practice may be so ingrained and automatic that you then play the J without due thought.

[aguahombre]

Fwiw, I believe than when a poster asks a question based on a premise, we should try to answer within context.

Some have done so, here. They have explained that the "discovery" jack is only a discovery play for the one who holds the KJ, and could create problems for the opening leader. Those who might, on-occasion underlead a bullet will all be in the "king" camp; that was not what the poster asked.

The other reasons for choice of King or Jack are covered very well. If pard never underleads, and you think you need the information about the queen right now at trick one, more than opening leader needs information about what to lead next, then Jack it. Otherwise King it.

[awm]

In many of the positions where playing the jack would leave partner on a guess as to who has the king... playing the king leaves a similar guess about the jack.

For example, say you lead from QTxx, dummy has three small, partner plays king and declarer wins ace. When you get in again, do you continue the suit (winning if partner has the jack or if declarer started AJ-tight) or switch and hope partner can play one through (i.e. if declarer started AJx or maybe AJxx). It seems like the same guess.

So I'd recommend playing the jack. This helps us know the layout and doesn't really hurt partner any more than playing the king would. Again, this assumes you are certain partner would not under-lead an ace on this hand.