[helene_t]

I believe the 1NT rebid is underloaded in natural systems. Especially if you play a weak notrump and especially is you play 4-card majors and/or up-the-line-rebids.

Consider the following Acol rebid (I am assuming a particular style, but that doesn't matter much):
1♣-1♠
?
1NT= 3334/2335, or 3235/3325 with a at least the queen in the doubleton. 15-16 points.
2♣=6 clubs, or 5 clubs w/o 3 spades, 11-15 points

As a consequence, the remaining bidding space after 1NT is rarely used, while there is a lack of bidding space after 2♣.

Since 2♣ takes up more bidding space than 1NT I think it should be stricter defined.

Suppose we let the 2♣ rebid promise 6. Then 1NT is either
- The usual 15-16 bal
- 11-16 with 1345/1435 or 1336 with a lousy suit.

After 1NT, responders rebid of 2♣/2♦/2♥ becomes non-forcing opposite the second variant, which 3♣/2♦/2♥ would be limit bids. A stronger responder can rebid 2N which would be forcing (probably GF).

After responder's 2♣, Opener passes with 11-14, bids 2♦/♥ with 15-16 and 1345/1435, and 2♠ with 15-16 bal. (The latter catters for responder having a weak hand with 5 spades (say 5332) and wants to take the 15-16 bal out to 2♠ but is worried about a 5-1 fit).

Any thought?

[jdonn]

Welcome to America! May I take your hat?

[nige1]

Acol Guru, Eric Crowhurst, invented many of the conventions, used the world over

For example, even when playing a weak notrump, Eric recommends a 12-16 notrump rebid. Then you can employ his eponymous 2♣ convention to refine the meaning
- 2♦/2♥/2♠ = 12-14 and as natural as possible.
- 2N+ = 15-16

Alternatively you can use one of the many modern Checkback variants.

My heretical view is that 5 HCP is too wide a range. Playing a weak notrump, I prefer
- 1N rebid = 15-17
- 2N rebid = 18-19
- 3N rebid = Gamble with long suit