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. Because formal debates follow established procedures and rules, a time keeper is necessary to keep track of each person's speaking time and the time given to teams to prepare arguments and rebuttals during the debate. Preparation time is usually set at one to two minutes between speakers. If a team takes longer, the time is subtracted from the speaking time. The time keeper has cards that he or she holds up to let debaters know how much time has passed.