If the responder holds a 5-card major, he could simply respond 1© or ª depending on which suit he holds. There is no point in telling the opener you hold a 4-card major.
It appears possible to show the 5-suiter, while transmitting at the same time some information about the strength of the responder's hand.
We have seen that 1© is a sohl-response which has several meanings.
One of those meanings (p:) points to a 5-card ©, while another meaning (q:) points to a 5+card in an yet unknown major suit.
Finally there is a meaning (r:) which points to a very weak 6-card in any suit and thus also in the major suits.
By using direct responses it is possible to describe the remaining types of hands holding 5-card majors.
Summarized we distinguish between:
With a 5-card ª the first response is always 1ª, which is forcing. By raising the response the opener shows a 3-card and his strength: 2ª weak, 3ª limit and 4ª strong (15-19 and singleton clubs). The responder on his next turn should show his strength.
With hearts it works the same, it only takes one more bidding round. The opponents may interfere, but Sohl does not get lost easily (Sohl doublet). If the the rebid to disappears, the opener still may conclude that the weak 5-card hearts (or spades in case of the double) was meant.
Without support the opener's rebid is 1NT (or PASS on his partner's 1NT) or his rebid is 2¨. Holding 4,5+ in clubs, diamonds it's better sometimes to call 2§
The 1¨ opening bid also allows for a 4-4 fit in a major suit. The convention is called MaD+++. This fit trial is executed by the opener in his first rebid, the sohl 1ª relay not being counted as a real bid.
This convention may be applied, when the opener possesses a singleton in clubs. Only then, he can hold one or two 4-cards in the major suits.
If the responder denies a 5-card major the strong (15-19) opening hand, or denotes a non fitting major, he describes his hand (16-19 hcp's, singleton clubs, 4-card suit bid, 4+card diamonds) by simple, without jumping, calling the major suit in which he hold the 4-suiter.
De Joker convention serves the same purpose as the MaD convention does after the diamond opening bid, finding a major suit fit. It would have been logical if we had given it a similar name: MaC, (finding a Major suit fit after a Club opening). You may still do so if you prefer. Right now I don't feel like changing everywhere 'Joker' into 'MaC'.
If you want to see examples of bridgames, in which the matter, treated above, is practiced, you should click on examples and choose for the appropriate convention or for any other typical call.
This convention is part of the MeRDe-complex ("MeRDe "= "Mean Repulsive Devices ", 'merde ' also is the french translation of 'shit '; it is used quite often by angry Frenchmen).
This complex consists of the next, void or singleton showing, conventions: SHiD+, SHiD+++, splinter, MaD+++, CUE, WievandeDrie and SHiCe