Acol (or Standard English) players can be faced with a bit of a problem with very strong hands (20+), which are essentially balanced but include a five card major. With so many points, a 1 level opener is risky because it could be passed out. On the other hand, an essentially balanced hand is unlikely to have the 8 playing tricks needed for a strong 2 opener.
The only remaining option is to open 2NT or, if it's really strong, an Acol 2§ (or Benjy 2§ or 2¨), followed by a 2NT rebid. Incidentally, have you agreed with your partner that any conventions, such as transfers, that you use opposite a 2NT opener also apply after 2§ followed by a 2NT rebid? If not, maybe it's something you should discuss. In this article, whenever I say 2NT opener you can take it as read that the same methods apply after a strong artificial 2§ or 2¨ opener followed by a 2NT rebid.
The danger with opening 2NT is that you could may miss a 4-major game if partner has three card support for your 5-card major.
Responder (opener’s partner) therefore needs to be aware that a 2NT opener is far more likely to conceal a 5-card major than 1NT does. Being aware is one thing. The real trick is knowing what to do about it.
This convention allows responder to check for both a 4-4, or a 5-3, major suit fit without going beyond 3NT. Opposite a 2NT opener, a 3§ response shows values for game and asks opener about his major suits.
In response to the 3§, opener bids:
| 3¨ | To deny a 5-card major but guarantee at least one 4-card major. | ||
| 3©/ª | To show 5 cards in the suit bid. | ||
| 3NT | To show no more than three cards in either major. |
Following the 3¨ response, both partners bid 4 card majors "up the line" until a fit is found or 3NT is reached. Once a major has been bid by either partner, a new suit at the 4 level is a cue bid agreeing the last mentioned major and 4NT is whatever flavour of Blackwood you normally play.
If you can get into the habit of always checking for a five card major before plunging into a possibly doomed 3NT you could save a lot of match points, and frustration.