[gwnn]

 Jinksy, on 2015-December-06, 03:42, said:

That seems more like a rationale for takeout doubles - now responder won't X with no points and the hand doesn't get bid.

Well, it was a rationale for asymmetric doubles vs symmetric penalty doubles. The rationale for making penalty doubles at all (not just symmetric doubles) is that sometimes you have a big fat trump stack and can't be sure your partner will make a takeout double, in particular, when the "short" hand is the 1NT opener. Takeout doubles also will fail to penalize some of the ridiculous "fits" such as 5-1 and we have 4-3, i.e., neither of us has a takeout double but both of us have kind of a penalty double. I know though that a lot of this can be avoided and I'm definitely for takeout doubles so you don't need to convince me.

[lycier]

 mgoetze, on 2015-December-04, 09:15, said:

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Our default is that doubles are takeout. Should this be an exception? If yes, can it be formulated as a more general rule (e.g. whenever they balance against our NT contract, all doubles are penalty?)

Yes,all doubles are penalty,or cooperative penalty at least.


It would be defined as penalty double to show long ♦ suit hold or have a ♦ constructure with some quick tricks.
While responder is a passed hand, especially with interference, the situations bcome more complicated, then if responder wanna to take some action,the best bet of responder is to make penalty double instead of takeout.. Responder promise to beat 2♦ contract,and at the same time it also implies opps can't find good fit.in fact this penalty double should be mainly for distribution.What else?

If defined as takeout,often difficult to find best fit.Even if both of opener and responder might find 8-card suit fit,also not easy for declarer to make this contract in the event of abnormal distribution.

Other option is to defined double by responder as cooperative penalty?

General speaking,whatever it is,it needs partnership agreement.