A method of showing length in any suit by means of a transfer used in conjunction with simple red suit (Jacoby) transfers. After 1NT,
2♦ = hearts
2♥ = spades
2♠ = clubs
2NT = diamonds
In the cases when responder shows a minor, opener has to choose whether to complete the transfer by bidding responder’s suit or to bid the suit/ denomination below that. It is usual to play one action as showing support for responder’s suit and the other as denying it. As is the case with red suit transfers, responder may have a weak hand (intending to pass opener’s transfer completion) or a strong hand.
On both hands, responder starts with 2♠, showing clubs.
On the first hand, responder intends to play in 3♣.
On the second hand, the rebid will be 3♥.
If you play four-suit transfers, you cannot bid 2NT to show a balanced hand wishing to invite game. The popular solution is to play non- promissory Stayman, starting with 2♣ on such hands.
An alternative solution is to play that a 2♦ response is either showing hearts or a balanced hand; with the balanced hand, responder has to make a specific rebid, normally 2♠.