Blackwood is a useful slam tool. However, inexperienced players rely on it too heavily. First, you should use it only when you are confident that you have the values for a slam and are just double checking that you are not missing two aces for a small slam, or one ace (or perhaps a king) for a grand slam.

Blackwood can also be unhelpful when you have a void. Look at today’s South hand. He opens two clubs and rebids two spades over partner’s two-diamond response. When partner raises to three spades, promising support and some values, South could jump to four no-trump, but after partner admits to one ace, what would he do? Does North have the useless heart ace or the invaluable diamond ace? South won’t know.

Instead, South should use control-bidding. Over three spades, he continues with four clubs, showing a first-round control in that suit (ace or void) and expressing slam interest.

Here, responder will continue with four diamonds, telling South about his ace. South could then jump to seven spades, because real bridge players don’t use Blackwood! Or he could cautiously check that partner really does have the ace. (Yes, South has a possible club loser, but, if necessary, he hopes to discard clubs from dummy on his diamonds and ruff the club six on the board.)

Here, after West leads, say, the heart king against seven spades, South ruffs and cashes the spade ace. When East discards, declarer cashes his top clubs, ruffs the club six on the board, draw trumps, and claims.