WE have looked at auctions where a player can make a limit bid at his first opportunity to call. A 1NT opening, or a limit raise of an opening bid of one of a suit, lead to simple sequences where partner can immediately decide whether game is possible or not.
Most auctions are not quite so simple: there is little point in limiting your strength if you do not know whether to play in no-trump or a trump contract; and, if the latter, which suit to choose.
North might be tempted to respond 1NT to partner’s opening bid. That is a limit response, showing 6-9 points. But it has a serious flaw: it denies holding a four-card major. The 1S response is not a limit bid – it could be anything from five to 20 points. Like the opening bid of one of a suit, it tells partner something about your distribution but does not limit your strength. It is therefore forcing – partner may not pass. The auction starts with two unlimited bids, but South has the opportunity to limit his strength at his second turn. With four-card support for partner’s major he will set spades as trump by raising. A single raise to 2S shows a minimum opener, 11-14 points; a jump raise to 3S shows 15-17 or so; with more he can raise to game, or follow a stronger sequence.
Reaching the 4-4 major sit fit marks a successful auction. South would pass a 1NT response – what else can he do? – and that would not play well.