[shevek]

Say it goes (no opposing bidding)

1♠ - 2♠
2N - 3♣
3♦

You are opener. You are pretty sure that your 2NT is the start of a short suit trial, singleton somewhere.
Partner doesn't alert. Perhaps she has forgotten, or is unsure; or you are wrong.
Then 3♣ seems like a hedge. In your mind, this asks for your singleton so it looks like partner is catering for both options.
Are you now supposed to alert 3♣?
Of course partner now has UI but it seems like she was on the right track anyway. Assuming you alert, can partner now read your 3♦ as showing a stiff diamond?

Thanks

[blackshoe]

In your system, 3♣ is a puppet, allowing you to show your shortage. If that requires an alert in your jurisdiction, then yes, you should alert it. In explaining it, you should avoid saying what the meaning of your next bid will be - just say something like "allows me to give further information about my hand" or some such. If your partner was expecting the alert, in spite of not alerting 2NT, then she can read 3♦ as a stiff. But if the alert was unexpected (because, perhaps, she had momentarily forgotten your agreement) then she cannot.

[jallerton]

blackshoe, on 2011-January-29, 21:35, said:

In your system, 3♣ is a puppet, allowing you to show your shortage. If that requires an alert in your jurisdiction, then yes, you should alert it. In explaining it, you should avoid saying what the meaning of your next bid will be - just say something like "allows me to give further information about my hand" or some such. If your partner was expecting the alert, in spite of not alerting 2NT, then she can read 3♦ as a stiff. But if the alert was unexpected (because, perhaps, she had momentarily forgotten your agreement) then she cannot.

In explaining the 3♣ bid, you should give whatever explanation is necessary to give a full description of partner's bid. Giving a vague explanation is misinformation (an infraction of Law 20F). Although this might happen to reduce the chance of partner receiving significant unauthorised information, that does not make it legal to give a vague explanation. If partner does happen to receive UI, then so be it; partner will just have to deal with it the best she can when it is her turn to call.

[blackshoe]

All I'm saying is that as I understand the convention, 2NT asks partner to bid 3C so that responder can further describe his hand. The 3♣ bid is a puppet, conveying no information about partner's hand. Information about what that description will convey is information about future calls, and I don't think not saying what that is constitutes MI.

[jallerton]

OK, but the opening post said that 3♣ asked for the singleton, which is not the same as a puppet. Presumably partner had other options, e.g. 3♠ rejects game tries whatever opener's singleton and another bid (e.g. 4♠) accepts all game tries whatever opener's singleton. Opponents are entitled to know that partner was interested which singleton you hold.

[blackshoe]

Fair enough.

[mycroft]

In my way of playing this, Jeremy is right - after 1M-2M; 2M+1, 2M+2 is "bid your singleton", and other bids are other meaning (3M "don't care", 4M "don't care", others "you're more interested in my 'help suit' than I am in your singleton". Yeah, responder asks 90% of the time, but it's not forced, or even "forced".

But I haven't played this for a long while - if I play non-trivial game tries, it's Kokish (where 2M+1 is "where would you accept a long-suit game try?", and other bids are direct short-suit)