Marty on Carding
Honor Card Discards and Other Thoughts
Honor card discards retain their standard meaning, depending on context.
i guess its arguable whether the 10 is an honor card for this purpose. i have never played it to be, but i have no authority to cite. this would be a great question to put to bobby goldman some evening when he's just hanging out in the lobby.
the conclusion your pd drew was correct if, arguendo, the 10 is an honor. what i was referring to in marty on carding was the following.
playing normal carding, and forgetting about the dummy for the moment, when your pd leads the A or K , the drop of the J shows a singleton. so from, e.g., J2, you have to play your 2. this is a "count" anomaly in std carding, but is "correct count" when playing upside down.
another honor card discard to know is the Q. The Q promises either the J, or a singleton (see how this fits with the J, above?) The reason it shows either is that what the Q *really* shows, is the ability to win the next trick (assuming it's not ruffed by declarer and that pd has the other high honor his lead suggested).
So the J shows a singleton, and the Q shows the ability to win the next trick. And this dovetails into my reasoning that the 10 is not an honor card for these purposes. If it were, then the J could either show the 10 or a singleton. But showing the 10 is virtually useless, because for this to be useful, pd must have the AK and Q in order to be able to underlead to you at trick two. Because this will come up soooo infrequently (and the opps can't have a singleton!), it has to be better to play that the J is specifically a singleton.
Your hand also brings up another subject on which you'll not find universal agreement -- what does your signal mean? Attitude, count, or even suit preference! Why suit preference? b/c you can easily argue that it would be folly to continue the suit when dummy hits with QJxxx, so it would be more important to help partner find the right shift. Speaking of switch, there's also Granovetter's pet system, the "obvious shift." The obvious shift system focuses on third hand's play at trick one, particularly when pd leads the A (or K from AK). 3rd hand either encourages or dis- the "obvious" shift. There are lots of rules to determine which side suit is the "obvious shift," which is its big drawback.
So, back to std. Is your 10 (assuming it is not an honor) a count card, an attitude card, or a suit pref.? My defaults are: count when declarer leads from either hand; att when pd leads, and suit pref when the suit cannot be led again (dummy is out). but this is not a default case, i don't think. i go along with the reasoning that pds attitude about a continuation is directly linked to his count (since all the honors are accounted for). With a doubleton, its the same anyway. With a singleton, no choice. With 3 or 4, that info is usefull to pd and can influence not only his play in that suit, but may also provide clues as to whether to go active or passive.
Suit pref is also a possibility, but i think count is more useful.
-- one man's opinion