The Second Negative Constructive (2NC) is the second speech given by the negative team, the fourth speech in the round, given by the second negative speaker.
It is the first part of the negative block and thus will only cover part of the 2AC.
Often the 2NC will bring up new arguments, to require the 1AR to cover more arguments in their 5 minutes (6 minutes in college). However, some judges consider it abusive to add new off-case arguments, as the affirmative only has five minutes to respond. It is not inappropriate to ask the judges view on allowing new arguments in the 2NC; after all it is a constructive speech.
Read more about this topic: Structure Of Policy Debate