Contract Bridge

Assume you’re in four spades and West leads the queen of hearts, obviously a singleton given East’s preemptive two-heart overcall. You win with dummy’s ace and lead a trump, on which East discards the eight of diamonds. This is an unpleasant development, as you now have two sure trump losers where a moment before you had a chance to lose only one and possibly even none.

Furthermore, your chance of finding West with the ace of diamonds has been greatly diminished by East’s diamond signal, which presumably shows the ace. But, despite the dim outlook, you still have a real possibility of making the contract. So you put up the ace of spades and cash the K-A of clubs, on which both defenders follow low.

You then continue with the seven toward dummy’s Q-10, West producing the nine.

You are now at the moment of truth. It is easy to see, if you look at all four hands, that if you finesse the ten, you make the contract, while if you play the king, you go down one. The question is how you can know, without seeing the East-West cards, that the ten is the right play and the king is the wrong play.

It is not difficult to prove that the ten is the correct choice. This is because if East actually started with the J-x-x of clubs, you cannot make the contract no matter how you proceed. If East has that holding and you play the king, West can trump the ten with his six of spades while you are discarding a heart or diamond, after which the defenders still have three more tricks coming.

But if you play for West to have started with the J-9-x-x of clubs, you are choosing a premise that allows you to make the contract. You should therefore finesse the ten of clubs, because it offers the only chance to get home safely.