Asking for aces (Blackwood)

If you and your partner have 32+ points combined, then you can go to slam (6-level). For this it is important that you don't miss 2 aces. To check this, the Blackwood convention was invented:

4NT (Blackwood)

• Asks partner how many aces they have
• You should only bid it if you know that there are at least 32 points combined

Responses to 4NT

• 5♣: 0 (or 4 aces)
• 5♦: 1 ace
• 5♥: 2 aces
• 5♠: 3 aces

In the 0 or 4 response, the 4NT bidder can see which option it is by counting the aces in their own hand

How to bid further?

Now you know how many aces your have combined

• If two (or more) are missing, then bid the desired contract on the 5 level. Partner should know to pass
• Are there one (or no) aces missing? Then bid the desired slam (6-level)
• Do not always bid on the 7-level when you know you're partnership has all aces, because you can still lose tricks then...