In contract bridge, a finesse is an attempt to win an extra trick by trapping an opponent's high card with the high cards of one's own partnership. Whether the finesse succeeds or fails depends on which opponent holds the high card.
In all our examples, South will be declarer; North, South's partner, will be dummy; and the play will be at notrump. Remember that the dummy's hand is visible to all players.
Suppose that after eleven tricks have been played, South needs two more tricks to make his contract. If the remaining cards look like this:
♠ 3 2
? ? ? ?
♠ A K
then there is no problem when North or South is on lead. South can just play the ♠A and ♠K, making his contract.
Let's give them a little less luck. Suppose the ♠K has not been played yet (West or East has it), and the remaining cards look like this:
♠ 3 2
? ? ? ?
♠ A Q
If South still needs to win both tricks, what can be done? South can try playing the ♠A and hope that the player holding the ♠K does not have a lower spade to pitch onto the ♠A. If he has a lower spade, South will be left with the ♠Q, which will lose to the ♠K.
Unless North-South held many spades before and expect one player to hold a singleton ♠K now, a better option for South is to take a finesse. To do so, the lead must be in the North hand. One of North's low spades is played. If East has the ♠K, he is stuck! If he plays it, South can win the ♠A, then in the next trick win the ♠Q. If North does not play the ♠K, South can play the ♠Q, then play the ♠A to the next trick. Either way, South wins both tricks.
What if West has the ♠K? Then the finesse will fail. When South plays the ♠Q, West plays the ♠K and wins the trick, defeating South's contract. West may also win a second trick; this will happen when his other card is not a spade. Therefore, if South only needs one trick, instead of both, he would be wise to play the ♠A immediately. This may cost him an overtrick, but the contract will be secure.
We have just looked at the most basic type of finesse. One also encounters repeated finesses, such as in the following hand:
♠ Q J 10
? ? ? ? ? ?
♠ A x x
If North is on lead and East has the ♠K, North-South can win three tricks here. Any of North's cards can be led (they are equivalent since they are of consecutive ranks). If East plays the ♠K, South plays the ♠A on top of it, and North's remaining cards are winner
s. If East plays a lower card, South plays a low card as well; North's card will win, and since the lead is still in the North hand, the finesse can be repeated with another spade.
There are many types of finesse, but you can go far with just the simple ones described here!