This version of Minor Suit Stayman (MSS) uses a bid of Two Spades s after opener bids one notrump to search for a minor suit game or the suitability of notrump.
2S requires at least game invitational values.
(a) an unbalanced minor suit hand
(b) no four card major
(c) a sngleton or void.
Opener bids
(a) 2NT -- natural and suggests controls in both majors. This does not deny a four-card minor, but suggests playing in notrump.
(b) 3 of a minor -- at least four cards in the minor and suggests playing in that suit.
(c) 3NT -- natural and promises controls in both majors
(d) 3 of a major -- shows a natural suit of a control in that suit. Opener has a four card minor, but is also interested in searching for 3NT. Responder bids 3NT with a control in the other major, bids 4C without one (to find the minor suit fit).
(e) 4 of a minor -- four cards in that suit and no wasted values in the majors (strongly interested in a miinor suit game and possibly slam if responder has a good hand.
Responder's rebids
(a) Pass -- to play (obviously)
(b) 3 of a minor -- if opener has rebid 2NT, this shows a five card minor and is non-forcing. If opener has bid 3C, 3D is forcing
(c) 3NT -- signoff
(d) 4 of a minor -- If opener has bid a minor, a raise of it is invitational. If opener has not bid a minor, or if responder bids the other minor at the four level, it is forcing.
(e) Any major suit bid -- shows shortness in that suit and is a slam try.
If opponents interfere after the 2S bid, opener may
(a) pass with nothing useful to say
(b) make the usual rebid, if possible
(c) double for penalty