Would you ever open 1NT with a 5 card major? Many players do and here’s an example of why it can be a good idea.
Suppose you are playing a strong 1NT opening showing 15-17 points and 5 card majors. That means that if you bid 1NT on the second round you’re showing 12-14 points and if you jump to 2NT on the second round you’re showing 18-19 points.
If you open 1H with the South hand, partner will bid 1S. Now what? You’re too strong to bid 2S and partner will expect youto have a four card spade suit if you jump to 3S. You can’t bid 1NT now because that would show 12-14 points on the second round and you’re not strong enough to jump to 2NT. Close, but it wouldn’t be quite right.
The solution advocated by many top players is to open 1NT even with a 5 card major.
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