Responding to partner’s
strongest bid, whether it be 2♣ or 2♦ should be the easiest thing in the world
because you either have a good hand or you haven’t – and you usually haven’t!
In the old days there were strict requirements for giving a positive and the
hand had to contain an ace and a king, or two king-queens, or three kings, but
those days have long since passed. To give a positive in a suit you need at
least a five card suit of good quality – something like KQJxx or better – and
upwards of about eight points, else just bid whatever your negative bid is. A
response of 2NT shows about 10/11 points in a balanced hand but I can never
remember having done that in fifty years of playing.
The auction above would be the one adopted by a pair playing either straight or Benji Acol and ordinary Stayman, asking for a four card major. The 3♠ bid shows spades but denies hearts, leading to the most obvious contract in the world and I would expect declarer to emerge with about eleven tricks.