This column should have run in Thursday’s edition.

The obligatory finesse is a play you make because there is no other choice. Its chance of success is normally not very good; rather, it is chosen because no other legitimate line of play is available.

Consider this deal where declarer must play carefully to make three notrump. First, let’s say South wins the eight of spades with the queen and leads a low diamond to the king, losing to East’s ace. East forces out the ace of spades, establishing his suit. South can now develop an extra diamond trick by playing the queen and another diamond, but this gives him only eight tricks, and he goes down one.

This line of play is not correct, however. Given the bidding, South should expect this result, so he should seek another approach. His only real chance for the contract lies in making three diamond tricks, and how he tackles the suit to accomplish this is where the obligatory finesse comes in.

Declarer sees 26 points between his own hand and dummy, so he knows East has at most 14 points for his opening bid. East is thus marked with the ace of diamonds, and South should shape his play to take advantage of this knowledge.

Obviously, if he leads a diamond to the king and East takes the ace, it becomes impossible to win three diamond tricks. Instead, South should try to lose a trick to the ace without sacrificing the king or queen. This can be accomplished only if East started with the doubleton ace.

So, after winning the queen of spades at trick one, South should cross to dummy with a club and return a low diamond, winning East’s nine with the queen. He then continues with a diamond and ducks whatever card West plays. This is the obligatory finesse. As it happens, East is forced to win the trick with the ace.

Tomorrow: Bidding quiz.