Take these finesse positions:

(i) K2                        (ii) AQ                          (iii) Q32
    -----                            -----                                 -----
     43                               32                                   A54

In each case you are trying to promote the underlined card (in the top hand). You must lead from the bottom hand intending to play that underlined card in the hope that the missing higher card is in the second player’s hand, playing before. A 50-50 chance.

The same principle applies here:

(iv)     J2
          ----
         AK43

Trying to promote the jack to win a third trick in the suit, you should lead a small card from the opposite hand towards the jack, hoping the queen is in the second player’s hand – as here:

(a)               

                        N 

                     ♦ J2

    W                                    E

♦ Q865                           ♦ 1097

                        S

                  ♦ AK43

After ♦ 3 lead, West can choose his poison. Rise with ♦ Q and North plays ♦ 2, later scoring ♦ J. Play ♦ 5 and North’s ♦ J wins.

Swap ♦ Q over to East...

(b)

                        N

                     ♦ J2 

    W                                      E

♦ 865                               ♦ Q1097

                         S

                    ♦ AK43

...and the trick would go ♦ 3, ♦ 5, ♦ J, ♦ Q and your 50-50 gamble has failed. But in that scenario [(b)], there is no way to promote ♦ J. Note, crucially, it does not help to make that most common of errors i.e. to lead ♦ J. I repeat it does not help, for if you lead ♦ J, East will cover with ♦ Q and you have achieved nothing. You cannot promote a card by leading it, for the opponents (either one) will simply cover it. Leading ♦ J here reduces your chances of promoting it from 50-50 to 0.

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