Fourth suit forcing

[sfi]

Ah right, so 1♠ is a game force which may or may not have spades. That's completely fine. What 2♠ would be, then? 5-6, gf? 5-6, nf? A forcing heart raise?

We play it as a splinter at the moment. It's never come up though.

[Zelandakh]

Ah right, so 1♠ is a game force which may or may not have spades. That's completely fine. What 2♠ would be, then? 5-6, gf? 5-6, nf? A forcing heart raise?

Most seem just to forget about it but I have seen it as a 2NT rebid without a spade stop, which covers one of the main holes left by making 1♠ game forcing. As sfi mentions, a splinter raise for hearts is another sensible meaning.

[Lovera]

The robots used to play 1♠ as natural and 2♠ as FSF, but now they play 1♠ as FSF and 2♠ as natural.

 

FWIW, I strongly prefer 1♠ to be FSF. If you play Walsh, responder will have a strong hand if they have four spades, so can afford the rare 2♠ bid. If you don't play Walsh, you can't afford to bid 2♠ with the FSF hands as they will have to cover a lot of ground since opener has shown little other than 11-18 points with 4-5 hearts.

 

If you play a Walsh style in which responder bids diamonds first with an invitational+ unbalanced hand with 4M and longer diamonds, then 1♠ has natural has merits, I suppose.

 

Anyway, as others have said, your third bid should be 2♠. I wouldn't call this "treating 1♠ as natural". It's just patterning out.

 

This FSF is an old but usefull convention. Among the answers this one raise is "rare" too! Is not the case of an up-to-date at the odiernly bidding that is actually competitive and much descriptive i.e. in support/raises or informative (i have an idea) ?(Lovera )