A finesse in bridge is the attempt to gain power for lower-ranking cards by taking advantage of the favorable position of higher-ranking cards held by the opposition. It is also 1. the attempt to take advantage of the location of the cards of the opponents, and 2. a play that makes such an attempt.
A finesse is used:
| 1. |
to avoid losing a trick. |
| 2. |
to gain a trick with the low-ranking cards. |
| 3. |
to prepare for a pinning play in the same suit. |
| 4. |
to prepare for a second finesse in the same suit. |
| 5. |
to keep a particular opponent off lead. |
| 6. |
to set up a safety play. |
| 7. |
to gain one or more entries. |
Practice Finesse
A finesse that is completely unnecessary and can only lose, and which can gain nothing. In other words, a practice finesse is a finesse which, if it works, gives you the same number of tricks you would have taken had you not taken the finesse.
The designation is meant as ironic, but this action can occur in certain situations such as the following, which shows the difference between a so-called Necessity Finesse and a Practice Finesse. A second designation is Malpractice Finesse.
Vulnerable: North-South
Dealer: East
It is possible that some bridge players, sitting West, might be persuaded to show the Clubs on the second round to reach an excellent 3 No Trump by East, but this West player, shrewdly aware of how much better off the partnership might be if he/she plays the hand, leaps to 4 Spades instead. North leads the 
King, possible the best lead for the defense, and West wins the first round. To the unpracticed eye this may look like a zero percentage play, but it wins if Clubs are distributed 5-1 and South has the short trump, which happens at least once for every five or six times this play loses.
Declarer is due to lose at least one trump, probably two, and this leaves the question of what to do with the Club losers. Diamonds come to mind, and West promptly finesses the 
Jack, which holds, improving the declarer's prospects considerably. West now plays off the two top trumps, with both defenders following. So far so good. As long as one defender can not ruff in before the fourth round of Diamonds, the declarer has time to discard two Clubs and make the contract, conceding two trump tricks and a Club.
If trump distribution were 3-3, of course, then a first round Club duck might have come in handy. Therefore if West repeats the Diamond finesse, the contract must make. However West leads a Heart and finesses the Queen. It holds, and West can still survive by returning to his hand with a Heart ruff and repeating the Diamond finesse. Instead West cashes the 
Ace, discarding a Club, and cashes the Ace. Unlucky again. The King does not drop. When West leads the Jack and South discards a small Heart, West still has at least a theoretical chance if he ruffs in hand and plays a trump. South may have erred by not ruffing and trump may be 3-3. But expert bridge players dislike taking advantage of defensive errors and West instead discards the 7, guaranteeing defeat.
However, what may seem apparent, may not be the case as shown in the following example:
Vulnerable: Both
Dealer: South
This example hand features something that looks like a practice finesse, but it was executed as a misrepresentation. After a Puppet Stayman sequence, where 2 showed no 5-card Major suit and 3
showed four Spades and five Hearts and game values, South landed in 4. West led a small Diamond. East won the Ace and returned the 3 to West's King. West shifted to a Club. The normal play now is to win the Ace of Clubs, discard a Club on the Jack, and execute a Heart finesse. If it loses, you win any return, draw trump and take another Heart finesse. This line of play fails because both Heart honors are offside.
South, the declarer, had another idea. South took what appeared to be a practice finesse when he finessed the Club at trick three. When the Jack held, he drew trumps, finessed again in Clubs, cashed the Ace and Jack, discarding Hearts, and took a Heart finesse. West won but was forced to return a Heart or give a ruff-sluff for the contract. The finesse in Clubs was not needed, or in other words the execution thereof gained nothing, in order to avoid a Club loser, since South's second Club could be discarded on the Jack, but it was needed to set up the strip and endplay.
If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.