I tend to understand ‘natural’ as the very opposite of ‘artificial’ (the latter being defined in the Laws).

2♦ non-forcing? That sounds like before World War Two.

I think 3♦ is an overbid; I like to see seven playing tricks for the bid.

CONCLUSION

Thanks everyone for your valuable contributions. This poll has yielded no consensus as to what ‘convention’ means or should mean. The term is no longer used (‘deprecated’) in the Laws and official regulations. Yet it is widely used in less than official settings. Apart from tradition, this could be because there is no single word for ‘artificial call’ nor for ‘partnership understanding’. Also, some languages have no common word for ‘treatment’.

Only a minority (24%) thinks ‘convention’ is just another term for ‘artificial call’. There is broad support (58%), but short of consensus, for the idea that a ‘convention’ is any agreement, artificial or natural, possibly synonymous with ‘partnership understanding’. Clearly a ‘convention’ may well be a defensive carding agreement, such as a signal. Some think a ‘convention’ can be a set of agreements rather than a single agreement.

With no consensus reached, I for me shall henceforth:
* avoid using the term ‘convention’ in official regulations or speaking thereof
* otherwise use ‘convention’ in the sense of explicit partnership understanding.

Feel free to follow suit.

2♣ then 3♣: showing a game force with long clubs and a second suit. 2♣ then 3♦ would be a game-forcing one-suiter in clubs (!). Game forces with diamonds as the long suit are included in our Multi 2♦, with the same rebids: 2♦ then 3♣ is long diamonds and a second suit, 2♦ then 3♦ the one-suiter.

As for bidding this hand as balanced, we could easily be down in 3NT (after a spade lead and missing the ♣A) while 6♣ is cold.

Depends strongly on the meaning of 1♦. If that is always or usually a five-card suit, 3♦ now as ‘natural’ does not make sense. If on the other hand 1♦ is ‘semi-natural’ and as of two or three diamonds, then 3♦ as natural stands out. (Please supply methods!)

I understand ‘natural’ as the very opposite of ‘artificial’, but apparently not everyone else does.

No votes for 1♣ – as that is not a voting option. (I open 1♣.)

In my book, partner can have as many as ten losers for his response. We respond on any five points or an ace, as appears to be modern expert practice.

Matter or not, deprecated (Ed) or not, the term ‘convention’ is widely used in bridge outside official Laws and regulations (at least where I live). Therefore it makes sense to agree on what we mean by it.

With its four quick tricks I see this hand as too strong for a 15–17 1NT, or at least borderline. In my methods I would then open this hand 1♣.

I appreciate that. I am, however, primarily looking for a consensus meaning of ‘convention’ that does not conflict with the definition and use of ‘artificial’ in the Laws.

By the way, ‘natural’ does not occur in the Laws either.

It appears that when it comes to defensive carding, the distinction between ‘natural’ and ‘artificial’ loses meaning.

I play this 2NT natural, because we play Raptor and our take-put double includes balanced hands on which others would overcall a natural 1NT.

2NT as Scrambling (two or three places to play) would not be very useful, as double already shows more than one place to play.

I would pre-alert the Strong Club itself, and a weak notrump (if any), not natural responses.

My € 0,02: I believe that when you’re behind, or enduring a ‘heat #3’, the best strategy is to play the best you can and aggressively but fairly normally. Doing something outright silly, like opening this hand, may occasionally work but is usually the surest way to lose.

I would consider 2♣ only at matchpoints and neither side vulnerable.

2♦: Multi including a game force in diamonds. Over 2♥, which tends to show (not guarantee) some spades, I will follow up with 3NT, showing about this hand. Over 2♠ I will rebid 3♦, showing a one-suiter.

Yes, at imps – not at matchpoints – I would have responded 2♣ with this excellent suit. I presume 7♣ for my vote can stand for this (it is not to be tacky).