From an examination of the leads, it will be seen that one main object is
to convey information to your partner. The king is led before the ace, so
that your partner may fairly conclude that, if the king wins the trick, you
hold the ace. If, after the king, the queen be led, he obtains an
additional piece of information. The science of Whist is in great measure
based on this principle of giving information to your partner by means of
the cards you play.
Among the conventions now universally adopted, perhaps the most important
is--