(Also check out the Theory Master Toolbox.)
Often times in a debate round, you will feel that your opponent is making an argument that is unfair in some way, whether they define a word poorly or they argue that you must prove that in every possibly conceivable scenario a certain action is ethical. Theory exists as a way to make an argument as to why that abusive claim should not be evaluated for the purposes of the round, and it has the added advantage of being an independent way through which you can win the round in general.
Despite its inherent usefulness, it is important to remember that theory when used poorly is very ineffective. Thus, it is important to have a full grasp on its role in the debate round and how its set up can create opportunities for you in round.
What exactly is theory?
Theory in its most contexts is debate about the rules of debate. Though it may seem silly to engage in those types of arguments, in reality there are no real established rules in LD besides the times and order of speeches. Thus, theory serves as a way through which you can resolve what types of practices are acceptable in a debate round and what kinds of practices should be rejected.
You should initiate theory when you believe your opponent is doing something that would break a rule that you think should be enforced. For example, if they define the death penalty as a series of NCAA sanction banning a collegiate sports team for playing for a year, you could argue that the rule they are breaking is that they should only use definitions that come from an academically relevant context.
In running theory, your job is to show what an important rule is for debate, show how they are breaking it, and finally prove why having that rule is important. Theory is normally run in a four-point structure with formal sections for the interpretation, violation, standards, and voter. This structure is known as the theory shell. While this structure isn't always necessary breaking down the argument in this way makes it easier to understand how theory is supposed to function and why it works the way it does.
Interpretation
The interpretation is the rule that you want to be considered for the purposes of the round. Further, the norm is to have a positively worded statement as your rule rather than a negatively worded one. So if you think your opponent shouldn't be allowed to have multiple criteria that link to their value, then you should say instead that they must have exactly one criterion. Further in general because you are establishing a rule that you believe they are breaking, you should stronger words like 'must' rather than weaker ones like 'may'.
Violation
The violation is the section where you establish how exactly your opponent violated the rule that you are arguing for. While in most cases it will be very apparent that your opponent is violating whatever rule you set up, you should try to make your violation as specific as possible.
An especially good strategy is to get your opponent to concede that they are violating this rule in cross-examination. During cross-examination, your opponent will not yet be aware of the rule that you will establish in the following speech, and as a result, they are likely to be very explicit in their statements. Having them make an explicit concession, makes your violation a lot stronger.
Standards
After you've established a rule and explained how your opponent broke that rule, the next step is to explain why that rule is important. This is where the standards section comes in. In general in debate, it is important to have rules to preserve two things in general: ground and predictability, and all types of standards, including things like time skew and strategy skew, are all fundamentally based in these two broader types of standards.
Ground
Ground is the standard most often cited in this section of a theory argument. Very generally, ground refers to the space available to make arguments. Thus, because certain interpretations (or rules) will always affect what types of arguments can and cannot be run, ground tends to be a very large issue.
The two main problems that arise in terms of ground are expanding and shrinking ground. In the case of the former, you shouldn't force someone to have to defend something too broadly - that would make a debate pointless as it would be impossible to discuss anything. When you shrink someone's ground, then they no longer have enough ways in which they can argue for their position again making the debate bad.
A problem with appealing to ground standards is that it is often very hard to measure exactly how much ground is appropriate and how much ground a certain interpretation seems to take away. Further, there is often the circular question of what exactly is valid ground to begin with.
Predictability
The other, more intuitive, general type of standard is predictability. This standard functions exactly as it sounds, and like ground comes in two flavors: in-round and out-of-round.
In-round predictability deals with knowledge of what your opponent will do in this round after they have already presented their arguments. An example of a violation of this type of predictability would be if in the 2AR, my opponent started talking about completely new arguments. In general, claims about in-round predictability have to do more with no way of knowing what strategy your opponent will take, making your strategy for the current speech impossible. For example, if my opponent had two criteria, I would have no way of knowing which one they would impact to, making my strategy for responding to their case impossible.
Out-of-round predictability conversely deals with being able to prepare for the round. For example, if my opponent started talking about the harms of global warming when we were supposed to be debating the death penalty, then it would be unpredictable but in a different sense than in-round predictability. In general, claims about out-of-round predictability tend to be weaker unless your opponent is truly not talking about the resolution rather than making an unexpected argument.
Voter
Once you've given a rule that is important and shown how your opponent is breaking that rule, you still need to tell the judge what they should do about it. In general, people believe that the winner of the debate is the person who argues their point more solidly, but that doesn't have many qualifications as to whether their arguments met some set of rules. Further, even if the rules are clearly established, there is no explicit articulation of what should be done when someone breaks a rule. This is where the voter comes in.
The two main voters that are used in debate are fairness and education. In the voter section, people argue that these two concepts are so important that a type of practice that makes a debate round unfair or uneducational should be banned.
Fairness
The argument for fairness is compelling and is cited slightly more often than the one for education. Debate is largely a competitive game, and people will only continue to play if it's fair. Further, an unfair debate undermines the judge's ability to accurately come to a decision. The ballot asks to determine who did the better debating, but if the round was unfair to begin with, that adjudication is impossible. As a result, the judge has an obligation to eliminate any unfairness before they evaluate the winner of the arguments.
Education
A similar type of argument can be made for education. The reason that schools fund debate and that debate is considered valuable is that it is largely educational. Students do research, practice, and work hard to ultimately learn more. Thus, if a style of argumentation detracts from the educational value of the round, the judge has an obligation to reject that as an educator and as an individual involved in debate.
(For more theory resources, including a complete set of competition-ready theory shells, check out the Theory Master Toolbox.)