The strong jump shift is a typical example of a convention that works well on the hands it was designed for. After for example 1 - 1 - 2, it is hard to show different types of hands with a good 6-card spade suit. The sequence 1 - 2 should be used to relieve some of this pressure. The problem with strong jump shifts is, they do hardly occur! Weak jump bids are much nicer. The definition is:
The last one may need some explaining: Assuming strong jumps, what do you bid with K87543 AQ5 6 QT8 after the auction 1 - 1 - 2?
There is no perfect solution. You can bid 2, which partner may pass with a reasonable hand with Honor and small support (making four), or you may bid 3, which will be too high opposite most minimum hands with a singleton . As part scores and games are more frequent than slams, the strong jump shift does not help you in this normal situation. Weak jump shifts do:
After an unbalanced rebid by opener (anything but 1NT and 2NT) after a 1-over-1 response, responder's rebid in the same suit shows:
Summary: If partner has no fit, you stay low (and safe) if you are not GF. If you have GF you can force it below game level so there is room to investigate what game is best or if slam is on.