Burden Of Proof

The burden of proof, often abbreviated "BoP", is a philosophical concept which denotes the party responsible for providing evidence of their position(s)http://en.wikipedia.org/wiki/Philosophic_burden_of_proof. On Debate.org, the burden of proof is most often assigned to either the debater who is asserting a particular positive position (often the instigator of the debate), or shared between both debaters (Pro and Con). Of course, debates frequently have no BoP at all. http://www.debate.org/forums/debate.org/topic/56116/1#1784074
It is advisable to establish whether there is a BoP--and, if so, what that BoP entails--before accepting a debate challenge, as this factor can be paramount to deciding the winner of the debate and leaving the BoP unspecified can lead to confusion for both debaters and judges. For this reason, Instigaters will often specify the BoP in her or his first Round (R1). To resolve a disagreement about the BoP prior to the debate, a potential acceptee of the debate can communicate with the Instigator via Debate Comment or Private Message (PM).
The BoP effectively instructs judges on how to interpret the evidence in the debate, and can ultimately influence final decision of who wins the debate (or the "argument" portion of the debate, depending on the debate settings). 
There is no default BoP assignment for debates. If no BoP is specified AND no other form of criteria/framework is specified, then judges must decide how to evaluate the arguments in the debate for themselves based on context.
==Unilateral Burden of Proof==
'Unilateral burden of proof,' or 'sole burden of proof,' is a situation in which one debater has a special obligation to provide evidence for a position, whereas the other debater technically needs only provide evidence negating that position (although providing additional evidence is advisable).
Note: Not all debates require traditional evidence. When the word "evidence" is used in this article, it is intended to indicate both traditional evidence and comparible rhetorical content (e.g. comparable arguments).
Note: A claim that has not fulfilled its burden of proof (BoP) is said to "lack warrant." 
Although a sole burden of proof (BoP) is more often assigned to the Instigater/Pro, it can technically be assigned to any debater. What is usually considered more important is that the debater with a sole BoP is making an affirmative claim. "Unicorns exist" is an example of an affirmative claim; it is the responsibility of the person asserting their existence to give evidence that they do. If the debater with the sole BoP provides no evidence, then Unicorns are presumed to not exist by default, and the debater with the sole BoP would lose by default. This situation highlights what is special about having the sole BoP: Situations that would normally be ties are considered as losses for persons with sole BoPs.
In most other ways, having a sole BoP is identical to having a shared BoP or no BoP. If the debater with the sole BoP gives evidence that it is likely that Unicorns exist, but their opponent gives stronger evidence that it is more likely that Unicorns do not exist, the the debater with the sole BoP would again lose the debate. However, if the debater with the sole BoP gives stronger evidence that it is more likely that Unicorns exist then not exist, the debater with the sole BoP would win the debate. IMPORTANT: If a debater with the sole BoP gives weak evidence that unicorns exist, but their opponent fails to negate that evidence entirely AND fails to offer evidence that it is unlikely that Unicorns exist, then the debater with the sole BoP would win the debate by default.
In other words, if the burden-free debater forgoes offering any evidence, she or he generally MUST negate 100% of their opponents' affirmative evidence to win. For this reason, forgoing constructive arguments is a risky endeavor, regardless of the BoP. In some cases, however, a judge may deem the net offensive evidence so insignificant as to be indistinguishable from a tie, and thus the debater with the sole BoP would lose.
In summary, when the BoP is on one side, the opponent has no obligation to make a constructive argument of their own, although it is highly advisable that they do so anyway. All that is technically necessary is for the opponent to successfully rebut all of arguments put out by the holder of the BoP; however, if the opponent forgoes constructive arguments, she needs to be sure to entirely negate all of her opponents' constuctive arguments.
==Bilateral Burden of Proof==
'Bilateral burden of proof' or 'shared burden of proof' is a case in which both debaters have to fufill a burden of proof (BoP). Technically, "shared BoP" indicates that the two debators are arguing in favor of two opposing resolutions. 
For example, an instigator may wish to debate that "Apples are better than Oranges" and for her opponent to debate that "Oranges are better than apples". In this case, a shared BoP would be perfect, because each debater would be equally obligated to defend their own claim and rebut their opponents' claim.
Whereas a debate with a unilateral BoP is concerned with the evidence for or against a single claim, a debate with a Bilateral BoP focuses on both claims. In these debates, the winning party is the one who successfully convinces the judge that their position is more likely than their opponent's position, using both rebuttals and constructive arguments. Unlike unilateral BoP, if there all constructive arguments are negated or equally balanced, then it is possible to have a tie.
It is interesting to note that in shared BoP debate, when one debater's position is the negation of the other--e.g. "Oranges are better than apples" and "Oranges are NOT better than apples"--it is, for (almost) all intents and purposes, exactly the same as no BoP. Indeed, many users use the term "shared BoP" to mean that one debater will take the negation of a position, even though a better term for such a situation is "no Burden of Proof."
==No BoP==
There are many debates that use neither a unilateral nor a bilateral BoP, but instead have no BoP. This option allows more flexibility than either unilateral or bilateral BoP. Some debates will use other weighing mechanisms as guides for judges in place of Burdens, such as Net Benefits, Utilitarianism, Ethics, Deontology, or Lives Lost. (Or, more creatively, tastiness, colorfullness, most creative use of adjectives, best rhythum and pitch, you name it!)
Usually debates with no BoP are judged similarly to debates with shared BoP--each debater defends their own position and attacks the other. However, unlike most shared BoP debates in which both debaters have specific positions to defend, for debates with no BoP usually one debater proposes a position and the second debater can contest that position in whatever way she or he chooses to do so. 
For example, if one debater proposed in a debate with no BoP that "Oranges are the best fruit," her or his opponent could respond by saying "Apples are better than oranges," "Banannas are better than oranges," and "Kiwi are better than oranges." However, the opponent is not obligated to defend that position. She or he could later say "Maybe bannanas aren't better than oranges, but even if they aren't they are at least tied!" In this way, no BoP is distinct from shared BoP because the opponent is not obligated to take any particular position (except perhaps the implied negation). 
No BoP is especially helpful for debates in which a particular policy is being discussed. In such cases, a tally of the benefits and disadvantages of a particular policy would be much more helpful than "proof" of something. Additionally, no BoP allows for the option of proposing a counterplan in a policy scenario.
Suppose, for example, that Pro suggested "The United States Federal Government should raise taxes on fur trading." Pro would likely list a number of reasons why raising taxes on fur trading would be helpful. Con would likely try to point out ways that Pro's claims about advantages are bogus and also point out disadvantages to raising taxes on furs. Additionally, Con has the option of introducing a competative counterplan. A competative counterplan is a counterplan that cannot be done alongside the proposed policy. An example of a compative counterplan that Con might bring up is "The United States Federal Government should ban all fur trading, and make fur trading illegal." This plan is competative because the United States Federal Government cannot both raise taxes on and ban all fur trading. Pro could then argue against this counterplan in much the same way Pro did the plan.
Note: If a counterplan is non-competative, it is subject to a permutation argument, or "perm." A perm points out that both the plan and the counterplan can be done simultaneously, and thus the counterplan really doesn't have anything to do with the debate. 
When judging advantages/disadvantages, or comparing approaches, or comparing values, debaters usually forgo having a BoP. Fogoing a BoP allows one to make arguments that are not about proving the existence of something, and allow one to have a counterplan. For that reason, BoP is most often invoked when a particular fact is being discussed. In that debate scenario, establishing a BoP is ideal. In other scenarios, having different criteria are generally preferred. 
That being said, it is nevertheless quite possible to have a debate about a fact(s) without a BoP. Supposing one debater wanted to debate "Unicorns exist," without a BoP. In that scenario, the debater merely needs to show that it is more likely that unicorns exist than it is likely that they don't exist (the implied negation). 
== References ==
Category:Debate.org
Category:Debate theory