[shevek]

We have this general agreement:
When partner doubles 2H or 2S for takeout and the next hand passes, 2NT is never to play. It's either Lebensohl or scrambling.
Trouble is, we are never sure which.

The usual agreement is "Lebensohl if game is still a chance".
However, this may need to be re-assessed if the 2NT bidder is limited.

For instance, with a 16+ 1C

1C (1S) no (2S)
X (no) ?

If passing 1S is nominally 0-4 (5), should 2NT now show complete crap, or "2 places to play", meaning something like
xxx, Qxxx, Qxxx, xx
looking to play any 8-card fit, converting 3C to 3D to show reds.

Compare
1C (2S) no (no)
X (no) 2NT

this seems better as Lebensohl since responder could have a decent but awkward hand that couldn't act first time, say
Axx, x, QJxxx, xxxx
bidding 3D with this to how decent vaulues, going via 2NT without SA.

[Free]

The first situation should definitely be a scrambling position imo. Either you had a trap pass (which will pass now) or you're broke. Looking for the best part score is probably more important to show the difference between 3HCP and 1HCP.

The second situation is more difficult, it depends on your agreements over 2♠ overcalls. If the range is still 0-7, then lebensohl is probably better. Nothing is perfect, but it's important to have clear agreements.

[helene_t]

Agree with Free. When you have failed to take action over a 1-level overcall, you are unlikely to have constructive values so Lebensohl is not so useful.

[shevek]

Okay, how about these:

(1S) X (2S) no
(no) X (no) ?

Are you limited enough by choosing not to act over 2S for this to be a scrambling auction?

(2D*) X (2S) no
(no ) X (no) ?

2D = standard Multi.
Likewise, you could have bid directly over 2S but didn't. Maybe the answer depends on the meaning of doubles.

[Free]

These are scrambling situations imo. The first one you chose not to act, partner doubles again to show extra's, but that doesn't change the fact that you didn't want to act in the first place. So there's no point in telling partner that you're weak - again.

The second one depends more on your defense against multi. For example, in my defense to multi, the 2nd Dbl is penalty in this auction.

[Gerben42]

I suggest you have (few!) specific situations for Lebensohl, then all other situations are scrambling.
For me the situations are:

1. 2-level opening - double (nf bid) 2NT
2. 1NT (overcall) 2NT
3. (opening) 1NT (raise) 2NT

Playing strong Club similar to #1 / #2 also:

4. 1♣(jump overcall) 2NT
5. 1♣ (pass) 1♦ (jump overcall)
Dbl (Pass) 2NT

I think that should be it.

[whereagles]

shevek, in addition to your agreement of

"It's lebensohl if game is still a chance."

you might want to add Robson/Segal's rule:

"It's scrambling when pard already had his chance to bid a lebensohl 2NT."

Applying this to

(1S) X (2S) no
(no) X (no) ?

(2D*) X (2S) no
(no ) X (no) ?

would result in 2NT now being scrambling. As to

1C (1S) no (2S)
X (no) ?

1C (2S) no (no)
X (no) 2NT

that would depend on whether 2NT over 1♠ or 2♠ would have been lebensohl or not.

[athene]

Play the default as scramble and just agree specific auctions where it's Leb. I don't think there are many where it shld be Leb. (Opps open 2M is the main one.)

One point is that if you play scramble, you can use that to show strength/not for the highest-ranking suit which is often the unbid major and what you need.

So for example:

Opps have some weird auction to 2♠ and pd doubles. 2NT is scramble.

Now if you bid 3♥ that is definitely good with hearts.

If you had bad with hearts you would bid 2NT scramble, pass if pd bid 3♥, and pull anything else he bid to 3♥.