The Blackwood Convention is used to avoid going into slam by mistake. 
The reply to the Blackwood 4NT request for aces is as follows:
- 5♣ — I have none or all 4 aces
- 5♦ — one ace
- 5♥ — two aces
- 5♠ — three aces
If all goes well, a 5NT request goes out to ask for Kings:
- 6♣ — I have no kings
- 6♦ — one king
- 6♥ — two kings
- 6♠ — three kings
- 6NT — all four kings
To understand the 4NT bid as conventional, rather than natural, is sometimes difficult. It is unquestionably conventional when the trump suit has already been agreed:
| North | South |
|---|---|
| 1♥ | 3♥ |
| 3♠ | 4NT |
| 5♥ | 5♠ |
| 5NT |
South’s second response is Blackwood asking for aces. North has two (5♥s). If the Blackwood bidder wishes to play in 5NT, he bids the next suit above his partner’s first reply (in this case spades over hearts). So South bids 5♠, which North had mentioned in the second round of bidding. And North has obligingly put him into a 5NT contract.
With the next hand it is North who has invoked Blackwood: 4NT asking for aces, then 5NT on the final bid asking for kings:
| North | South |
|---|---|
| 1♠ | 3♣ |
| 3♠ | 4♠ |
| 4NT | 5♥ |
| 5NT | 7♣ |
After the second request responder may choose to jump straight to slam without further ado on the following card holding:
South as responder
♠ A
♥ 10 7
♦ Q 9 2
♣ A K Q J 9 6 5
North shows 13-19 points and a minimum of four spades with his 1♠ opening bid. South’s jump shift to 3♣s shows 16+ points and a minimum of four cards in clubs. So far so good. North’s rebid at 3♠ shows he has five cards in spades and also 16+ points. With a combined minimum of 32 they are now slam going. The only question is which contract? South’s rebid of 4♠ is forcing and North bids 4NT to ask for aces. South replies 5♥ to tell opener he has two. North then asks for kings (5NT). With a powerful 7-carder, South ignores the question and leaps into Grand Slam in his club suit.
When to use blackwood
The Blackwood bidder must bid small slam if only one ace is missing. Bid 4NT when you hold one ace and ♦s are to be trumps; two aces when ♣s are to be trumps. Avoid Blackwood when you have a singleton.
Bidding sequences—which show Blackwood?
| Bidding sequences - which are Blackwood? | |||
|---|---|---|---|
| 1] | North | South | Notes |
| 1NT | 3♠ | ||
| 3NT | 4NT | Not Blackwood | |
| 2] | North | South | Notes |
| 1♠ | 3♠ | Suit is agreed | |
| 4NT | Blackwood | ||
| 3] | North | South | Notes |
| 1♥ | 3♥ | Suit is agreed | |
| 3NT | 4NT | Blackwood | |
| 4] | North | South | Notes |
| 1NT | 3♠ | ||
| 4♦ | 4NT | Blackwood: Difficult one here, but North’s 4♦ infers agreement with South’s ♠s. | |
| 5] | North | South | Notes |
| 1♥ | 3♦ | ||
| 3♥ | 4NT | Although South has not agreed ♥s, his jump to 4NT (out of the blue) must be Blackwood | |
| 6] | North | South | Notes |
| 1NT | 3♣ | ||
| 3NT | 4♦ | ||
| 4NT | Not Blackwood, but an insistence on playing in No Trump | ||
| 7] | North | South | Notes |
| 2♠ | 3♦ | ||
| 3NT | 4NT | Responder’s 3♦ is a positive response, and his 4NT rebid must be taken as Blackwood | |
| 8] | North | South | Notes |
| 2♠ | 2NT | ||
| 3NT | 4NT | Compare this with the previous example. Here, the 2NT reply is a negative response showing weakness, so his 4NT cannot be Blackwood | |
| 9] | North | South | Notes |
| 1♠ | 3♣ | ||
| 3NT | 4NT | A jump shift to 3♣ shows strength. The bid of 4NT over Game call clearly indicates Blackwood | |
| 10] | North | South | Notes |
| 4♥ | 4NT | The 4NT reply to a pre-emptive opener is not Blackwood | |
Finally, with intervention, despite the partnership having agreed trumps, the 4NT call cannot be construed as Blackwood.
| North | East | South | West | Notes |
|---|---|---|---|---|
| 1♥ | 1♠ | 3♥ | 3♠ | |
| 4♥ | 4♠ | No bid | No bid | |
| 4NT | The 4NT here is a competitive call and cannot be taken as Blackwood | |||
Replies to Blackwood
| Example | North | South | Notes |
|---|---|---|---|
| #1 | 4NT | 5♦ | As already shown the 5♦ shows one ace held by South |
| #2 | 4NT | 6♦ | But this, for example, would show one ace and a void |
Interference during Blackwood
| North | East | South | West |
|---|---|---|---|
| 1♦ | 3♥ | 4NT | 5♥ |
After this 5♥ interference, North will bid as follows:
| North | Notes |
|---|---|
| Double | If he considers the partnership will get more for penalties than for slam, he will double |
| Pass | If he has no aces he will pass |
| Otherwise he will show his aces adjusting the Blackwood scale to start after the interfering suit bid of 5♥ (ie at the cheapest level): | |
| 5♠ | To show he has one Ace |
| 5NT | 2 aces |
| 6♣ | 3 aces |
| 6♦ | 4 aces |
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To continue reading go to: Other conventions
By Nigel Benetton – based on the UK Acol Bridge Bidding System
Last updated: Thursday, 24th June 2021