[Dinarius]

An interesting variation on all of this “what would East do with J, x,?” is the following:

In a recent Pairs event, I was South playing in 4♠️ with a 6/3 fit. I had K, 10, x, in Dummy opposite A six times.

East (a very good player) won the first trick and immediately played Q♠️. I won with the A♠️ and finessed the 10 losing to the J♠️. I made 10 tricks for average minus. No one in the entire room made this East ♠️ switch. So, every South played for the drop and claimed +1.

East’s reasoning was, “I have no easy exit card, so I may as well play a trump since I’m going to lose them both anyway.” As I played it, she only lost one.

Should I have still played for the drop in that situation?

D.

[sfi]

Dinarius, on 2018-November-06, 06:06, said:

Should I have still played for the drop in that situation?

The real answer to your question is "it depends". It depends on the bidding, the lead, the play, the level of your opposition, the ability of the overall field, your opponents assessment of your level of play and, most importantly, what the entire hand is.

Ignoring all that, let's assume that 4S is a normal contract, there is no opposition bidding to guide you and you simply want to draw all the trumps with no losers. From a purely probability point of view, East's holding of Q is more likely than QJ because sometimes they would lead the Jack from the second holding (making your play the favourite). Balancing that, it is less likely East would switch to a singleton queen than to QJ doubleton. But probability plays a much smaller role than the logic of the rest of the hand. East's play of the SQ should be viewed with suspicion, and you need to work out why they might have switched to it.

Going back to the suit in question, if you play it without them leading one first you would simply start with the Ace. If East drops an honour the finesse is a 2:1 favourite to win (this is straight restricted choice). If not, you plan to play for trumps 2-2.

The fact nobody did that suggests either you had the 9 in your hand and it was more convenient to play for a singleton honour in West rather than East, the field is very bad or something else is going on in the hand.