Partner might have the heart JACK, that is it, as between dummy and you and the spade jack partner has already shown, own 16 hcp remain out. If partner has a queen, then declarer has at most 14 ( i am assuming 15-17 1NT). PArtner rates to have 5+
♠ for the spade discard. We can count 2D, 3S, 3H, 2C for declarer. IF he has 4
♥ an 11th trick shows up if he has the heart JACK. If he lacks the heart jack, and has no more than 4
♥, he will have to turn to clubs for TWO extra tricks.
I am going to return an un-ingenous diamond. The reason is
not psychological, it is based upon bridge logic. I don't know where the club TEN is, but if declarer has it, we are in some trouble if declarer has 4
♣'s -- assuming the club "x's" are truely small. Declarer knows about our 5 diamonds. Should he win AKQ in both majors, we will show out in each giving our full distribution (2-2-5-
4). Such a discovery play will give declarer the easy option (percentage play) to play us for the club queen should he have, say AT8x or AT9x (2-1 odds we have the queen).
Can he play the same way if we return a diamond? He could, but it removes removes his freedom to try both majors and benefit from a discovery play should PARTNER turn out to have the long clubs. Let's imagine the following hand....
So
♦ back, the hell with psychology. Without a diamond, declarer should have a cake walk to 12 tricks when he has clubs to the TEN.
(I guess you could argue to return high heart showing two to allow him to get count on hand so that you would be tellign him you have 4
♣, which you might do as a double cross when holding xxxx of clubs, but most will still go with the odds, should they discover the distribution).
Defending against
1NT - 6NT