User:Brian/Bridge/Responding to a one-level minor opening
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Partner's bid shows something like 12 to 21 total points and denies a 5-card major. If partner bid diamonds, they almost always have 4+ diamonds, but rarely only 3. If partner bid clubs, they usually have 4+ clubs but sometimes only 3. Therefore, you should only raise partner's minor with at least 4 cards in that minor. But wait! Before raising partner's minor, you should first explore the possibility of a 4-4 major fit. Partner doesn't have 5 of a major, but might have 4 of a major, so if you yourself have a 4+ card major, you should try to find a fit. If you can find a fit in a major suit, it is better to play in the major suit than in a minor suit.
Very weak hands
A very weak hand contains 5- HCP.
I have a very weak hand but 5+ card support for partner's suit → Consider making a preemptive raise to the 3 level. (The more unfavourable the vulnerability, the better your suit needs to be.)
Otherwise → Pass.
A minimal hand contains 6 to 10 HCP.
I have a minimal hand and a 4+-card major → Bid 1 of the major. (With both majors, bid hearts first.)
I have a minimal balanced hand → Bid 1NT.
I have a minimal unbalanced hand, I am on the low end of the range, and I have 5+ card support for partner's suit → Make a preemptive raise to the 3 level.
I have a minimal unbalanced hand, I am on the high end of the range, and I have 4+ card support for partner's suit → Raise partner's suit to the 2 level. (That is, a single raise is stronger than a double raise. This is the inverted minors convention.)
I have a minimal unbalanced hand, partner's suit is clubs, and I have 4+ diamonds → Bid 1♦.
None of the above apply → Usually bid 1NT. This can sometimes be a lie, showing an unbalanced hand, for example if partner opened 1♦ and you have some unusual distribution like 2-1-3-7, or (more likely) you're too strong for a preemptive double raise or too weak for a single raise. In the latter cases it's a judgement call whether to bid 1NT, upgrade, or downgrade your hand.
An invitational hand opposite a 1-level minor suit opening contains 10/11 to 12 HCP. Typically, even with a 8-card fit in the minor, you will try to play in notrump if possible, so avoid counting extra points for shortness.
I have an invitational hand and a 4+-card major → Bid 1 of the major. (With both majors, bid hearts first.)
I have an invitational hand with stoppers in the other 3 suits → Bid 2NT.
I have an invitational hand with 4+-card support for partner's minor → Raise partner's suit.
I have an invitational unbalanced hand, partner's suit is clubs, and I have 4+ diamonds → Bid 1♦.
I have an invitational balanced hand, or my only shortness is in partner's suit → Bid 2NT. Partner will think you're likely to have stoppers in the other 3 suits, which might not be the case, but hey, sometimes that can't be avoided (like when a 1NT opening is raised to 3NT). And you probably have at least a partial stop, since you have a decent amount of HCP, right?
Otherwise (I have an invitational unbalanced hand and none of the other cases apply) → This case is annoying and luckily doesn't come up too often. It means partner opened 1♦ and you have length in clubs, e.g., a 1336 distribution (and the singleton spade isn't an ace). If you are a passed hand, respond 2♣. If you're an unpassed hand, you can't respond 2♣ because that would be game forcing. So instead you have to use your judgement. You can take a risk and respond 2NT anyway, or you can downgrade your hand and bid 1NT, which is (obviously) more likely to make than 2NT or 3NT.
A game-forcing hand contains 13+ HCP. Note that even with an 8-card fit, you will want to try to play in 3NT, since some additional strength is usually needed in order to make a 5m contract. In rare cases you'll have to stop in 4m because you have neither the stoppers for 3NT nor the strength for 5m, so "game-forcing" doesn't really mean forcing to game, but rather "forcing to 3NT or 4 of a suit".
I have a 5+-card major → Bid 1 of the major. With two five-card majors, bid 1♠ (you will have an opportunity to show hearts later).
I have a 4+-card major → Bid 1 of the major. With two four-card majors, bid 1♥ (so partner still has the chance to show spades).
I have 5+-card support for partner's minor and a void or small singleton in a side suit other than clubs → Make a splinter bid.
I have 4+-card support for partner's minor → Raise the minor. (Don't worry—this is forcing.)
I have stoppers in the other 3 suits → Bid 3NT.
I have 4+ cards in the other minor → Bid the other minor at the cheapest level (1♦ or 2♣).
Otherwise → (I don't think there is an "otherwise". If you have at most 3 of each major and at most 3 of partner's suit, then you must have 4 of the other minor suit.)