By default, Wbridge5 opens strong notrump, so inverted minors is disabled. Wbridge5 includes inverted minors because weak notrump is also available.
Inverted minors originates from Kaplan–Sheinwold. Inverted minors is popular in East and Southeast Asia due to popularity of Precision Club, based on K-S with strong club, inheriting the weak notrump opening.
Nowadays, many ones open strong notrump according to somewhat American. However, some of them still employ inverted minors. Inverted minors has pros indeed, easily found by searching “inverted minors”. Hence, I list its cons as balance.
Garbage 1NT response
Weakness of inverted minors is not on itself but the 1NT response modified because of inverted minors. The 1NT response may have the following meanings:
- Constructive 1NT
- At least 6 tricks expected if both minimum.
- Garbage 1NT
- Only 5 tricks expected if both minimum.
When partner opens 1♠, 1♥, or 1♦, not to miss a probable game, garbage 1NT is on as the opponent passes.
If inverted minors is agreed, without intervention, garbage 1NT is always on.
If inverted minors is off, a constructive 1NT is ensured over 1♣ opening even if intervened, as there is always a better call i.e. a suit or pass. Respond 2♣ with a weak 3-3-3-4 because the opener often has 4+ clubs.
- If 1♣ ensures 3+ clubs
- With minimum strength, the probability of only 3 clubs is 21.5%.
- If 1♣ can be 4-4-3-2
- With minimum strength, the probability of exactly 3 clubs is 20.4%，4-4-3-2 5.19%.
Weak 4-card support dumped as garbage
Express 5-card support at 3 level preempts, but 1NT with 4-card support is much less preemptive. Is there so much difference between 2 of a minor and 1NT, as 1NT is just one or two bids lower? Let’s consider the following.
The point is not whether to escape, but the positive pass. Notrump sucks for the declarer, 6.06 tricks taken on average. 1NTxS−3 is more tragic than 3NTE= unless favorable vulnerability. In addition, the total notrump tricks may be less than 13.
If 2♣ were responded, east must have had clubs to pass, positive advances elevated onto 2NT. Preemption is force opponents bid high with strong hands. Although 2♣ is only one bid higher than 1NT, pass and cuebid are pushed onto 2NT.