The defenders use the same techniques as declarer does to develop tricks, i.e. promotion, length, finesse, the trump suit, and discarding losers on winners. Because the defenders can’t see each other’s cards, defensive signals help, so the cards they play to each other at certain times will mean something. It's possible to give a defensive signal any time you have a choice of cards to play to a trick, but remember that your first job is to win the trick!
(1) Attitude Signals
If partner has already won the trick, or if the trick was won in dummy before you can play, now it's time to show partner whether you liked their lead or not. The card you play to the first trick, and later your first discard, will show partner whether you want them to keep playing that suit. The card you select is known as an attitude signal.
The most popular methods are called low or high encouraging. This means, if you choose low to encourage ("low I like"), the smallest card you can afford will tell partner you liked the lead, and more importantly, that you would like that suit continued. High is the opposite, i.e. the highest card you can afford says you would like that suit continued. Make sure you and partner are on the same page with this!
NB: The person who leads simply follows the recommended guidelines. It’s the leader’s partner who signals their “attitude” to the lead. Partner leads the ♥3, dummy wins the ♥A, and you have ♥K92. You would like hearts continued, hoping to win your ♥K. If playing low to encourage, the correct card to play is the ♥2. If playing high encouraging, it’s the ♥9.
The other types of signals you could use with partner during the defence are:
(2) Count Signals
There are times when it's clear you wouldn't be showing attitude ( i.e. liking a suit and/or wanting it continued). mainly when declarer is playing their own suit in no trumps. Now it's better to show partner how many cards you hold in the suit being played. Why is this? Perhaps partner holds the ace and wants to break declarer's communications with dummy by winning their ace when, and only when, they know declarer will have none left to reach dummy.If you show how many cards you hold in the suit, partner can work out how many declarer started with, and will know how many times to "duck" (not take) their winner.
Play high-low to show an even number of cards, and low-high to show odd. eg you hold 9853. Play the 9 followed by the 3, to show an even number. With 983, play the 3 first, followed by the 9, to show an odd number. It’s important to recognise when the situation calls for attitude or count. Attitude should have priority. Count usually happens when declarer is playing their suit.
Here's a situation: Dummy
Partner leads ♠3 against 3NT, and dummy plays ♠2. You play ♠Q, third hand high. This wins the trick, and you lead back a spade, returning partner's suit. Declarer must win this trick with ♠A. Declarer will play on diamonds, to promote them. But there is no outside entry to the suit in dummy. If West doesn't take their ♦A until the third round, declarer will not have a diamond left to cross to dummy's diamond winners. The only way West will know when to take their ♦A is if they know how many diamonds declarer started with. If East plays the ♦8 first time, and then ♦2 next, they will be completing a count signal, and showing partner that they hold a doubleton. West is able to deduce that declarer started with three diamonds. W holds three, dummy five. East has just shown two, so declarer must have started with three diamonds. (3 + 5+2 = 10, there are three left in declarer's hand).
Count signals help too when it is clear that partner can't want attitude, e.g. when defending a high contract, like 6NT or 7NT.
Although using signals is helpful, there is no substitute for your own logic at the table. Take notice of what's in dummy, how declarer is playing the contract, and realise that sometimes you don't need a signal at all. It's all there at the table to see!
Want more information? This book and cards will help you learn about defence.
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