We all sympathise with that constantly uttered regret, "Oh, partner, if I had only known that you had that suit," and Bridge players the world over have felt the need of some conventional play that would indicate to the original leader an adequate reason for a change of suit.
The Change the Suit Call is a new convention designed to overcome this difficulty, one that will save countless tricks and rubbers, and one that will tend to minimise the dealer's acknowledged advantage in playing the two hands.
The convention is as follows: When the original leader's partner has a great suit, one that is established or one that may be established by a single lead through the dummy hand, an echo should be made in the suit led by the dealer. In other words, an echo in the adversary's suit is a command to the original leader to abandon his own unestablished suit and to switch to his partner's declared strength.
The idea is of course based on the call for trumps in Whist, in which game an echo in any plain suit is a command to the partner to lead trumps. In Bridge it is used principally at no-trump and its application is limited to an echo on the dealer's lead.
The reader will naturally ask, "How, when but two suits have been led, can I determine which of the two remaining to choose?" The cards in the leader's hand combined with those in the dummy will usually simplify the selection. Should the leader hold a re-entry in one of the remaining suits it is obvious that he has been asked to lead the other. When it happens that both the leader and the dummy are weak in both suits, the preference should usually be given to the one in which the combined hands contain the fewer number of cards.