[barmar]

Here's a good example where "no agreement" doesn't mean "natural": You forget to discuss which form of Blackwood you play, and then one of you bids 4NT. Are the responses traditional 4-ace Blackwood, RKC 3014, or RKC 1430? It's almost certainly one of these, but everyone is guessing which one.

[pescetom]

blackshoe, on 2018-June-11, 14:07, said:

If you have reason to expect that your partner will understand a conventional meaning to a call you make when you have no explicit agreement about the meaning of that call, then you need to examine why you have that reason. If it's because you know that he plays it that way with others, or you know that he knows that you play it that way with others, or one or both of you have done it before, then this information needs to be disclosed, because you have an implicit agreement.

I recognise that. That's why in the situation of the OP I would only bid 2♥ if we had agreed to play transfers in this situation, or at worst that I know that he plays it that way with others, or I know that he knows that I play it that way with others. I believe we have an explicit (or at worst implicit) agreement and that he will disclose it by alert.

blackshoe, on 2018-June-11, 14:07, said:

But the basic reason why I said you're mistaken is your assumption that "no agreement" implies "natural". "No agreement" implies there is no agreement. It might not be logical to bid something intending a non-natural meaning when your partner doesn't know what you're doing, but people do illogical things all the time.

Yes, I take your point here, thanks. I would never bid ♥ with no ♥ on the mere hope that partner would take it as ♠, but the world is large and various.

barmar, on 2018-June-12, 08:57, said:

Here's a good example where "no agreement" doesn't mean "natural": You forget to discuss which form of Blackwood you play, and then one of you bids 4NT. Are the responses traditional 4-ace Blackwood, RKC 3014, or RKC 1430? It's almost certainly one of these, but everyone is guessing which one.

It's a rather extreme example, both because it is one of the few situations where the bid is very unlikely to be natural and because these things are at the top of the list to discuss before playing. And if it did happen for some reason then I wouldn't be the one to bid 4NT. But yes, I would have to guess the responses to partner's 4NT.

[blackshoe]

"Byzantine Blackwood".
"What the heck is that?"
"Well, it's… complicated."
"So what does his response mean?"
"You know, I don't remember."