[sceptic]

pass pass 1 major pass 1NT

is this a forcing situation in 2/1 as a passed hand

or is it semi forcing in 3rd or 4th seat

or is it forcing by agreement only

[awm]

There are few "forcing" bids by a passed hand, since the initial pass limits the values.

Playing 2/1 I would assume that 1NT is "semi-forcing" meaning that it could be a hand (balanced or unbalanced) with up to invitational values. A truly forcing notrump by a passed hand would be a rather unusual agreement and certainly not one I'd assume without discussion.

[helene_t]

The reason why 1NT is forcing by an unbalanced hand is that responder may have, among others:
1) a very weak unballanced hand that wants to play some other partscore, such as 3M
2) a very weak hand with 3-card support
3) an invitational hand with length in a minor (or hearts) that wants to force unless opener has a misfit
4) an invitational hand with 3-card support that wants to force unless opener has a balanced minimum

1) and/or 3 (depending on preempt style) would propably have opened with a preempt. 4) can use Drury and for that reason 2) can raise since with Drury, a simple raise is 5-8 (or such) rather than 8-10 as after a 1st/2nd seat opening.

Therefore a forcing 1NT by a passed hand would not be very useful.

Besides, if opener has a subminimal 3rd seat opening, you may come to high if he can't pass 1NT. And some people like to open on a good 4-card M with less than 12 HCP in 3rd seat. Then you don't have a rebid.

[Kalvan14]

1NT by a passed hand is forcing by agreement only (e.g., if you want to keep some invitational balanced raises: IMO, if you play Drury it solves your problem). The real issue is what to do with clubs in an invitational hand (diamonds or hearts can be shown as a 2/1). Not a big deal, in particular if opener will keep the bidding open with a good opening (14/+).