(Except as specified in the Analysis of Leads, pp.64-71).
For, otherwise, your partner is uncertain where the highest lies, and you and he may play two winning cards where one would have sufficed. For instance, if, with queen, knave, ten, you lead the ten, your partner may put the king on it, but he certainly would not on the queen. In addition to this, if there is anyfinessingto be done in the suit, it can only be by your partner. By finessing is meant playing an inferior card though holding a higher one of the suit, not in sequence with the card played. Thus, to continue the illustration of the sequence of queen, knave, ten. You lead the queen. Your partner has the ace and others. He will not put it on, but will finesse by playing his smallest card; and if the king lies to your left, that card is completely hemmed in. Had you led the ten, your partner would have put on the ace, and the king have been freed.
On the other hand, if you lead from an under sequence, you should lead the lowest, the reason being that, in this case, you wish your partner to put on his highest card. For example, with king, ten, nine, eight, you should lead the eight and not the ten, as if your partner's highest card is the knave, you wish him to put it on that he may not afterwards block your suit by retaining a commanding card of it. Or,suppose your partner's best card is the queen, the lead of the ten would probably induce him to finesse, and thus give the adversary a chance of making the knave the first round, and of retaining the ace in hand, although you and your partner hold two honours in the suit. If your partner puts on the queen, you are still able to finesse the nine when the suit is returned, and this is much more advantageous than your partner's passing the ten. In the first place, the finesse is postponed to the second round, when, more cards having been played, you have more data to guide you as to the policy of making the finesse; and, in the next place, if you have a choice as to whether you or your partner shall finesse in your strong suit, it is, as a rule, more advantageous for you to do it. For, as already explained, it conduces to the establishment of a suit for the strong hand to retain the command of it, and for the presumably weak hand to play his highest cards.
With sequences neither at the top nor at the bottom of a suit (intermediatesequences), the card to lead is the lowest of the intermediate sequence.
Players who adopt American Leads will, however, select the fourth-best card when leading a low card from suits of more than four cards, whether or not the suit contains an under sequence, or an intermediate sequence (with the sole exception of ten, led from king, knave, ten, and small). Thus, from king, knave, ten, nine, whether accompanied by the eight or by smaller cards, they lead the nine; and so on for other combinations. (SeeAppendix A, pp.281-6).