The proposition is the arguable statement. The negative team argues against the proposition. The negative team usually argues in favour of the current position or situation, as the proposition is usually in support of a change to the way things currently are. There are two types of debate propositions. The key in debating is the proof of arguments.
Proof can be in the form of either logical reasoning or evidence.
Logical proof is based on common sense and common knowledge. Value debates usually use this type of proof, which is more subjective. Debaters use logic and common sense to build a convincing case. Evidence includes facts and statistics from reliable sources. Action or policy debates usually use this type of proof, although they may use both types.