In SAYC my partner bid 1 NT showing 15-17 HCP (no void, no singleton and only one doubleton). I was holding a hand of 10 HCP with 5S, 5H, 2D and 1C. Using Jacoby transfers should I have responded 2D (showing 5H) or 2H (showing 5S)
This is mostly a matter of agreement.
The reason this is so, is that what you decide to do with a 5-5 game forcing hand would effect other hand types.
Here are some hand types the responder can have:
5-4 majors game forcing. 5-4 majors invitational
5-5 majors game forcing 5-5 majors invitational.
They are multiple ways of bidding:
For instance, some folks play 3H response to 1NT as invite with 5-5 majors and 3S response as GF with 5-5 majors. This allows them to transfer and bid the other suit to show some 5-4 hands etc.
So there is no one way to bid this, and is something you need to agree with your partner.
In bridge, the rule is to bid the lower suit in order to proceed more slowly.
Here, the "lower" bid is two diamonds, partner transfers into two hearts, and then you bid two spades, staying at the "two" level when you show your second suit. It depends on the partnership style, but such bids at the two level are often treated as "invitational," and not forcing.
If you bid two hearts first and partner transferred into two spades, you'd need to bid three hearts to show your hearts. More to the point, a bid at the three level would be considered by many to be game forcing and show slam interest.
Whatever "subsystem" you use should be agreed with partner beforehand.
Playing SAYC there is always the possibility of partner making an error - both my partner or partner's partner. This is a different situation that two strong players with a very solid system understanding.
With 10 points you are entitled to show both majors, creating a game forcing situation - however with a weak partner it is advisable always bid 2D first (showing Hearts) instead of the other way around, because a rebid of 2S will be unambiguous to a weak partner, but a return to 3H might be misunderstood.
All else equal this also happens to be best practice, as Tom Au has already mentioned, but in practice there are advantages in this situation to bidding your weaker suit first - middle honours in partner's hand are gold, and he learns fo their value sooner this way.
In SAYC, continuations from Jacoby in other suits are all game forcing.
If, after the transfer is accepted, responder bids a new suit, that is natural and game forcing.
As such, both
1NT - 2D
2H - 2S
and the inverse
1NT - 2H
2S - 3H
are game-forcing. Without any other agreements, there is technically no difference in the system; I would suggest that the choice of transferring to spades first is the weaker option, and transferring to hearts first is the stronger option, as it gives you more room to discuss possible slams.
As you are a minimum game forcing hand (10 points opposite 15-17), you should make the weaker choice, and bid 2H to transfer to spades. Since partner is guaranteed to have a 3 card fit with one of these two suits based on your rules for opening 1NT, you don't need to worry about ending up in 3NT.
Of course, it is preferable to have a superior agreement with partner than the basic SAYC agreement, as this hand pattern (5-5 Majors opposite 1NT) is frequently a slam-going hand even with only 10-12 points, if things line up properly. You likely can't find that with only Jacoby, while the direct bid of 3S (GF 5-5 Majors) as Aryabhata suggests would be quite helpful in possibly finding that slam.
This is too long for a comment but it could be of interest to somebody.
I do not play the SAYC but, with my partners, what we use for describing a 5-5 distribution after the partner open 1 NT is a bid at the level of 5 in the shortest suit (for H and S) or at the level of 4 (for C and D).
For example :
- 1 NT - pass - 5 C means 5 H + 5 S (void or singleton in C)
- 1 NT - pass - 5 D means 5 H + 5 S (void or singleton in D)
- 1 NT - pass - 4 H means 5 C + 5 D (void or singleton in H)
- 1 NT - pass - 4 S means 5 C + 5 D (void or singleton in S)
This implies no hope for a slam.
Using this convention for almost 30 years, we think it is very precise and we have good results with it.
I personally would not bid this using Jacoby transfers, but using Stayman. By bidding 2C in response to the 1NT opening, you ask if opener holds a 4-card (possibly 5, depending on your definition of a 1NT opening) in a major. partner responds with:
- 2 Diamonds: none
- 2 Hearts or 2 Spades: that one, or
- 2 NT: both majors.
If he has no majors, you can still bid 2H. Having asked him about his 4-card Majors, him denying and you still bidding one makes it at least 5 cards long. 3NT is still an option at this point, even with your distribution.
If he does have one (or both) of the majors, pick one for game.