At Euros we proposed the following standard for knifing, which is an articulation of a rule of thumb that many (but not all) good judges use: Teams should only contradict the team before them on claims that are plainly impossible to make persuasive to a reasonable person with common sense and a conscience. These include gross factual errors and morally repugnant ethical positions.
Upon further consideration, I think that rule is problematic. (I say that, as the person responsible for writing the briefing document that publicly advocated it.) There are several problems with it:
- The rule involves a tricky judgement as to what the bounds of possibility in debating are. Is it possible, for instance, to make extreme consequentialist positions persuasive to the hypothetical reasonable person? Will she ever buy that we may eat babies that good may come? Maybe there is a way to make the position persuasive, but the judge hasn't thought of it yet.
- The rule specifies a standard for behaviour but not the penalty for breaking it. All good judges are agreed that knifing cannot be grounds for an automatic fourth (I do hope we can agree to this on a priori logical grounds, since obviously more than one team can knife). One can contradict claims of varying degrees of centrality to the opening team's case.
- The rule commits teams to defending driftwood in the opening team's case. If the opening team has made a weak claim that has been thoroughly rebutted, it may often be a more persuasive argumentative strategy to concede that claim, and instead argue a point that contradicts it. ("Ok, so we concede that America bombing Syria will have a non-negligible effect on its government infrastructure. In fact, there is a risk that it will in fact break the government into warring factions and plunge the country into anarchy.")
Because of that (and at the risk of adding to the existing muddle of rules of thumb) I'd like to propose a new standard for when it is acceptable to knife. Namely: Closing teams that contradict a claim made by the opening team should be treated as though they had conceded entirely the opening team's claim. The degree to which they are penalised should depend precisely on how that changes the overall persuasiveness of that teams case.
To take some illustrative examples, this means that a closing team that contradicts a weak or unpersuasive claim from the opening team, in order to replace it with a stronger argument, should be counted as thereby having made a net contribution to their side's case. (Though, obviously, not as much a contribution as would be counted if adding this argument would have involved no knifing at all.) By contrast, a closing team that contradicts a strong argument, central to the opening team's case, in order to replace it with a weak argument, should receive a penalty for having done damage to their side's case.
This straightforwardly addresses all three problems that I illustrated above. (It is much easier for judges to decide which of two contradictory arguments is more persuasive, and how much so, than to decide when teams cross the line into "impossible" claims that trigger the possibility of knifing.) I think it's a better standard, that means that the Opening teams arguments do affect and constrain what the Closing team can say, but only to the extent that those arguments are useful and persuasive. It may, however, introduce new problems. I'd be interested to hear what experienced judges think about it.