Description of a bid that is helpful and forward going, seeking to find the best contract.
This is opposite to an obstructive or pre-emptive bid, the main aim of which is to make life difficult for the opponents. It is also opposite to a sign-off. Constructive bids are usually invitational (partner may pass) or sometimes forcing for one round rather than game forcing.
All of East-West’s bids in this sequence are constructive:
