[Douglas43]

pescetom, on 2021-May-17, 10:49, said:

To each his own poison, but that sounds perverse to me. Even if you do not want to play FSF as an unconditional game force, surely it makes sense to promise a rebid: that way the person replying can bid in economy, giving you the shape information you need to decide what to do next.

This route allows the FSF bidder to get information about partner's range (after 1♥ - 1♠ -2♣ - 2♦* opener with a minimum and a diamond stop bids 2NT, with a better hand and a stop bids 3NT). So yes there is less economy in space, but responder might not have a useful bid over 2NT. It also allows for FSF bidder to confirm a GF hand when they have one.
But as you say there is no one "right" answer.

[Gilithin]

In traditional Acol, 4SG at the 2 level was INV+.
In SEF and Forum D, 4SF at the 2 level is GF if above 2 of Opener's suit and INV+ if below.
In modern Acol and most versions of 2/1, 4SF at the 2 level is always GF.

All 3 variations have their pros and cons so pick your poison. I think this thread though is about 4SF INV-only and GF hands instead make a jump rebid. That is quite a different concept to the more common ones, which was presumably the reason for having a thread for that rather than on 4SF in general.

[the hog]

What about another structure altogether?Here the fourth suit is a transfer, transfer, as suggested by Jassem, instead of the traditional fourth suit forcing. For example over the following sequence:

1♥ 1♠

2♣ 2♦ ( transfer to 2H)

2♥

Now:

pass = weak to play in 2♥

2♠ = weak wants to play in 2♠

2NT+ game forcing.

Where this becomes nice is

1♥ 1♠

2♣ 2♥/2♠ are mild invitations, 2NT is invitational, 3♣/♥/♠ are serious invitations.