eagles123, on 2013-March-22, 07:30, said:
would 2♣ not be raise in spades?
No - with 4
♠ you just raise spades to the appropriate level. The prototype textbook hand for cue bidding 2
♣ is something like a 3442 shape with 19+ points, but can include other shapes if you are really strong. What you are essentially saying is "we may have enough points for game, but I don't know where". It does not promise another bid. You can cue bid with four spades with some absolute monsters, but you then support spades strongly later.
You should generally prefer the natural bid if one is available, so here the choice is between 2
♦ and and 2
♣, intending to follow with 3
♦ to show the monster. 2
♦ should show about 18-21 points so we are a little bit heavy, but 2
♣ will lead to problems when partner has a very weak hand, since he will generally just bid 2
♠, expecting us to have three.
2
♦ will occasionally lead to a missed game, but it would be my choice.