When an opponent opens the bidding with 1 or 1, the immediate overcall of 2NT shows at least 5–5 in the
minor suits (that is, at least five clubs and at least five diamonds). If the right hand opponent (RHO) of the partner of the 2NT bid passes, that partner is expected to bid the minor suit that he prefers at the three-level. The unusual notrump applies the principle that when the natural meaning of a bid is not generally very useful, it is profitable to agree that it means something somewhat opposite. That is, while natural notrump bids show a strong hand with balanced distribution, the unusual notrump shows a weak hand with very unbalanced distribution. If the 2NT bidder bids again freely, then it shows a
strong two suiter. To distinguish the weak and strong holdings, many partnerships agree
not to use the unusual notrump for intermediate hands (about 12 to 14 points); they would simply overcall with one of their suits and show the other later if the bidding offers a chance. However, for two-suiters, many players apply
losing trick count (LTC) instead of point count, as it more accurately depicts the offensive trick-taking potential of the hand. With LTC in effect, the required strength is about 4.5–7 losers, the latter only in favorable vulnerability. Similarly, a 4NT overcall shows an extreme two suiter (usually at least 6–5, often 6-6 or 7–6) and enough trick-taking potential so that a 5-level contract can be made, or a sacrifice will likely be profitable. It shows the same two suits as 2NT would show. Note that 4NT is "unusual" only when the opponents open the bidding; otherwise, 4NT is normally played as the
Blackwood convention or a quantitative invitation to 6NT. The
Michaels cuebid is a similar convention which is used to show a two suiter with one or both
major suits. To counteract the unusual notrump, the opening side may employ
unusual vs. unusual. ==Modifications==