This article will look at one of the fundamental requirements for bidding a natural NT, typically 1NT, 2NT or 3NT.
The starting principle is - if we bid No Trump, we promise a stopper in the opponents suit.
Lets consolidate that idea with some examples and then look at an exception to the rule, which actually happens quite frequently.
The need for a stopper
A classic example is as follows
Example 1
Here you have bid 1NT. You are confident that you have at least 1 stopper in the opponents suit, spades. You probably have two stoppers! However, the requirement isn't to have 2 or more stoppers, just one is enough to allow you to bid 1NT.
Why do I need a stopper?
It is okay to declare 1NT without a stopper and lose say 5 or 6 spade tricks, especially if you then proceed to take the next 7 or 8 tricks! However, what happens if partner raises you to 3NT! In 3NT we need to make 9 tricks, so we cannot afford to have the opponents with the first 5 or more tricks.
Rule: When partner bids No trump, you can rely on them having a stopper in the opponents suit (If the opponents have bid).
It might be worth briefly mentioning, if the opponents are silent throughout, you don't need stoppers, for example
Example 2
Here we don't have stoppers in spades or clubs but we still bid 1NT - the stopper rule only applies if the opponents have bid a particular suit. "If they have not bid it, there is nothing to fear".
Lets look at another example, it applies in all auctions.
Example 3
Here partner has bid 2♠ which is natural and forcing (Responder's first change of suit is forcing - see Is that bid forcing? Responder's first bid.) We bid 2NT which is a simple and natural bid - showing balanced shape and a diamond stopper.
Lets look at what happens when you're on the other side
Example 4
Here you can confidently bid 3NT knowing that partner has promised a stopper with the 1NT bid.
The rare exception
There is a situation, which requires partnership discussion, but typically goes like this - "when partner forces you to bid on the 1 level, 1NT does not guarantee a stopper".
Lets look at what I mean by that
Example 5
Partner's 1♠ forces you to bid, so pass is out of the question. You don't have any sensible bid, so you just bid 1NT as the best way to describe your hand, but not perfect. You were forced to bid, and didn't have a better alternative. This is a rare situation, but by far the majority of the time when you bid No Trump, you are showing a stopper in the opponents' suit.
Read next: Is that bid forcing? Responder's first bid. · Responder's First Bid: Raise, New Suit, or No-Trump · Opening 1NT: When to Open and When Not to