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Today, I want to discuss the role of real-world examples — known among LD debaters as “applications” — in debate rounds. Some coaches and competitors insist that every contention in an LD case requires an application; indeed, during rebuttals, some competitors encourage judges to reject arguments for the sole reason that they do not include applications. In my view, this is misguided. Some arguments require applications, but others do not.

To distinguish between arguments that need applications and those that don’t, we must introduce a distinction between a priori knowledge and a posteriori knowledge. A priori knowledge is knowledge that is based on reason or intuition, rather than observation. For example, knowledge that all circles are round is a priori, because it is possible to have this knowledge without observing any circular objects. Since circles are round by definition, it would be pointless to measure every circle you could find to determine whether they were round. Another example of a priori knowledge is moral knowledge, such as the knowledge that torturing an innocent person is wrong. No double-blind, peer-reviewed scientific study could establish this, and even if one could, you would not have to perform a study in order to know that it is true. Your conscience tells you that torturing the innocent is wrong, in the same way that your reason tells you that all circles are round.

A posteriori knowledge (also sometimes called “empirical” knowledge) is knowledge that is based on observation. For example, the claim that the COVID-19 vaccine is safe and effective is an a posteriori claim, because it can only be settled by conducting scientific studies. Our knowledge about cause-and-effect relationships is almost always a posteriori: in order to know which events cause which other events, we must observe them. For instance, we now know that smoking cigarettes causes lung cancer because we have observed that one follows from the other.

Whether an argument requires an application depends on whether it is an a priori argument or an a posteriori argument. For example, a debater who argues that confiscating property is morally wrong because it violates the human right to self-ownership makes an a priori argument, so he does not need an application. After all, how could a scientific study or a historical account show that confiscating property is morally wrong? On the other hand, a debater who argues that upholding the right to property is necessary to prevent tyranny makes an a posteriori argument, since it is possible to test his claim through observation. So, he needs an application.

Since a priori claims do not require applications, it is possible to write a competitive LD case with no applications by appealing exclusively to a priori premises. This is why the common objection, “My opponent provided no applications,” is inadequate: it is not enough to point out that your opponent failed to appeal to concrete evidence. You must also explain why the judge should have expected him to provide concrete evidence. It is reasonable to expect concrete evidence for the claim that free markets promote economic growth, or that cognitive-behavioral therapy is an effective method for tempering criminal behavior. It is not reasonable to expect concrete evidence for the claim that seizing a person’s property violates Kant’s Categorical Imperative, or for the claim that justice requires proportionality in sentencing.

On the other hand, most good LD cases make a posteriori claims, so most of them should include multiple applications. This is why the common response to the above common objection, “This is LD, and LD is about philosophy, so I don’t need applications,” is equally inadequate. While it is true that LD resolutions often center on a priori claims, that does not give you license to make a posteriori claims without evidence.

In conclusion: you should not be asking, during a debate round, “Did my opponent offer enough applications?” That is because what counts as “enough” is entirely dependent on the content of the arguments offered during the debate. What you should be asking is, “Did my opponent offer enough of the appropriate kind of evidence for his claims?” In other words, did he offer good a priori reasons for a priori claims and good a posteriori reasons for a posteriori claims? If not, then point it out. But if so, do not criticize him for failing to offer the wrong kind of evidence.

Noah McKay is a debate coach and sourcebook author at Ethos Debate currently pursuing graduate studies in philosophy at the University of Edinburgh. He has coached individuals and groups in LD for five years.