In this article we introduce an argument model: a set of terms for analyzing arguments by naming their parts. There are various argument models in the academic literature on argumentation theory and related fields but none provide us with precise definitions for all the concepts behind our algorithms for improving online conversations. So we will define those concepts here.

Anatomy of an Argument

Our model incorporates the basic ideas from the influential Toulmin model of argumentation first introduced in 1948, but uses a simpler model with more modern terminology.

Claims

A claim is a declarative sentence that people can accept or reject (agree with or disagree with). This definition is broad enough to include not only descriptive (or empirical) claims about reality, such as the universe is expanding (what is), but also normative claims about goals, such as we should go to the beach (what should be).

In argument involves two claims:

• A conclusion: the claim in dispute.
• A premise: the reason given to accept or reject the conclusion.

There is also a third, unstated claim called the warrant: the implied claim that the premise, if accepted, is a good reason to accept or reject the conclusion.

Premise and Conclusion

For example, during a jury trial, the prosecutor might claim that (𝐵) the defendant signed a confession to support the claim that (𝐴) the defendant is guilty. In this case (𝐵) the defendant signed a confession is the premise, and (𝐴) the defendant is guilty is the conclusion

An argument may be worded in such a way that the premise is unclear (sarcasm, etc.), but there is general agreement among argumentation theorists that there is always a premise hiding in an argument.

Since any logical combination of premises can be treated as a single premise, we will speak of an argument as always having one (possibly compound) premise. For example, the claim BMWs are unreliable and overpriced when used in an argument is treated as a single (compound) premise, even though it can be broken down into to distinct premises (e.g. BMWs are unreliable and BMWs are overpriced).

It is easy to confuse the term claim with the term premise or conclusion – especially since different authors use these terms differently. In our model, a claim is any declarative statement that can be agreed with or disagreed with. A claim can also take the role of premise or conclusion in some argument. In the example above, 𝐴 and 𝐵 are both claims, where 𝐵 takes on the role of premise, and 𝐴 takes on the role of conclusion. If the defense contested the premise 𝐵 with some new claim (e.g. (𝐺) the signature was forged), 𝐵 would take on the role of conclusion in the new argument, and 𝐺 would take on the role of premise.

The Warrant

The warrant can be thought of as a second unexpressed premise that links the expressed premise to the conclusion. For example, the warrant of argument (𝐵) the defendant signed a confession might be (𝐶) if she confessed, she must be guilty!

The warrant can be thought of as belief that “justifies the inferential leap from premise to conclusion” (to paraphrase Toulmin). It is related to the Aristotles concept of enthymeme.

People don’t find it necessary to explicitly state the warrant. They assume the link from the premise to the conclusion will be evident to their audience (otherwise, they would be more explicit).

Even if the arguer does (pedantically) explicitly express what they see as the warrant of their argument, there still is always an unexpressed premise of the form if this premise and warrant are true, then this conclusion is true. This is the idea behind Carrol’s paradox, though we don’t need to go down that Rabbit hole here. To keep things simple and practical, we assume that the premises always leave something unexpressed (or conversely, we do not assume that premises are always perfect logical syllogisms from which the conclusion infallibly follows). We must therefore always allow room for questioning whether the conclusion follows from the premise, which means we assume every argument has an implicit warrant. And this warrant, just like the explicit premise, is fair game to argue over.

Summary of Model

The diagram below shows a sample argument with labels for the three parts of the argument.

So in the diagram above, the argument in support of conclusion (𝐴) the defendant is guilty, has two halves. On the left is the premise (𝐵) the defendant signed a confession. This is the claim that has been explicitly made. On the right is the warrant: the claim that 𝐵 is a good reason to accept 𝐴.

This is a very simplified model. There are many concepts from the field of argumentation theory literature that we don’t need to address here (rebuttals, backing, etc.), and our definitions may lack nuance. But these definitions are meant to provide not a comprehensive theory of argumentation, but a basic vocabulary that allows us to have clear discussions about certain otherwise nebulous concepts.

Types of Arguments

Opposing and Supporting Arguments

The warrant of a supporting argument is the claim that the premise is a good reason to accept the conclusion, and the warrant of an opposing argument is the claim that the premise is a good reason to reject the conclusion.

Note that an opposing argument is just a supporting argument for the negation of the conclusion. (𝐵) the defendant signed a confession supports conclusion 𝐴, but opposes conclusion (not 𝐴) the defendant is innocent.

Premise Arguments and Warrant Arguments

Making the distinction between premise and warrant allows us to cleanly distinguish between premise arguments and warrant arguments.

In the chart below, we have added two arguments that oppose 𝐵. The argument with premise (𝐺) the signature was forged, opposes the premise (𝐵) the defendant signed a confession. It is a reason asserted for believing that 𝐵 is not true. We call this a premise argument. The argument with premise (𝐶) the defendant retracted her confession, opposes the warrant of the argument with premise 𝐵 – the claim that 𝐵 is a good reason to accept 𝐴. We call this a warrant argument.

Argument Notation

Identifiers for Premise Arguments

We represent an argument that supports conclusion 𝑋 with premise 𝑌 using the notation:

$$ \text{𝑋◂-𝑌} $$

Note we place the premise after the conclusion.

For example, referring to our jury trial argument graph, the argument $\text{𝐴◂-𝐵}$ could be expressed in plain English as the fact that the defendant signed a confession is a good reason to believe that she is guilty.

We represent an argument that opposes conclusion 𝑋 with some premise 𝑌 using similar notation, but with a hollow arrow:

$$ \text{𝑋◃-𝑌} $$

For example, the argument $\text{𝐵◃-𝐺}$ might be expressed in plain English as the fact that the signature was forged is a good reason NOT to believe that the defendant signed a confession.

If the claim 𝐵 is also used as the premise of some other argument, that would be a separate argument. For example, an argument that opposes conclusion 𝐻 with premise 𝐵 would be $\text{𝐻◃-𝐵}$, which is not the same argument as $\text{𝐴◂-𝐵}$, even though it uses the same premise

Identifiers for Warrants

We represent the warrant of the argument $\text{𝐴◂-𝐵}$ using the notation

$$ \text{𝐴◂𝐵} $$

It’s easy to confuse the warrant $\text{𝐴◂𝐵}$ with the argument $\text{𝐴◂-𝐵}$, especially since the notation is similar. To reiterate the difference: the warrant $\text{𝐴◂𝐵}$ is a claim that 𝐵, given it is accepted, supports 𝐴, whereas the argument $\text{𝐴◂-𝐵}$ is the claim that 𝐵 should be accepted, and that it supports 𝐴. Or in other words, the warrant says “if the defendant signed a confession, that would be a good reason to believe she is guilty,” whereas the argument says “the fact that the defendant signed a confession is a good reason to believe she is guilty.”

Identifiers for Warrant Arguments

Premises such as (𝐶) the defendant retracted her confession oppose the warrant of the argument $\text{𝐴◂-𝐵}$. We notate warrant arguments like this:

$$ \text{𝐴◂𝐵◃-𝐶} $$

This identifier has the same form as the identifier for a premise argument, except that the conclusion (the part on the left of the $\text{◃-}$ or $\text{◂-}$) is a warrant.

In plain English, this argument might be read as the fact that the defendant retracted her confession is a good reason to believe that she is not guilty even if she confessed.

Argument Graphs

Given a set of arguments that have been made in some situation, we can create a graph that shows relationships between the arguments. The graph below represents our sample argument, now using our new argument notation.

Each argument in this graph has one outgoing blue arrow, pointing to the argument or claim it supports or opposes. Using the same convention we adopted for argument identifiers, solid arrow heads represent supporting arguments, and hollow arrows heads indicate opposing arguments.

Note that the blue arrows in this graph contain redundant information, because the relationships between arguments are revealed in the identifiers themselves.

Note also that the entire graph could be reconstructed entirely from the identifiers of the leaf nodes.

Because cycles are hard to deal with, we will assume all argument graphs are acyclic, thus our argument graphs will always be DAGs.

Review of Sample Argument

Here is a brief review of the sample argument shown in the argument graph above using the terminology and notation we have introduced so far:

• The claim (𝐺) the signature was forged opposes the conclusion (𝐵) the defendant signed a confession. Since 𝐵 is the premise of the argument $\text{𝐴◂-𝐵}$, $𝐺$ opposes the premise of $\text{𝐴◂-𝐵}$. So $\text{𝐵◃-𝐺}$ is a premise argument.

• The claim (𝐶) the defendant retracted her confession, opposes the warrant of $\text{𝐴◂-𝐵}$. It says that even if the premise 𝐵 were true, it is not a good or sufficient reason to support $𝐴$. So $\text{𝐴◂𝐵◃-𝐶}$ is a warrant argument.

• Both $\text{𝐵◃-𝐺}$ and $\text{𝐴◂𝐵◃-𝐶}$ oppose their conclusions: the premise and the warrant of $\text{𝐴◂-𝐵}$, respectively. Thus they both oppose the argument $\text{𝐴◂-𝐵}$.

• In the example above, we consider $\text{𝐴◂-𝐵}$ itself to be a premise argument, because it is supporting the claim $𝐴$. While claim $𝐴$ does not play the role of premise in any argument in this graph, it is pragmatic to call $\text{𝐴◂-𝐵}$ a premise argument because we always assume that $𝐴$ could be playing the role of premise in some larger argument graph.

Argument Threads

Definition of an Argument Thread

An argument can support or oppose the warrant of another warrant argument.

In response to $\text{𝐴◂𝐵◃-𝐶}$, someone might argue (𝐷) guilty people always say they are innocent. This argument would be written as $\text{𝐴◂𝐵◃𝐶◃-𝐷}$.

And of course there could be a response to this argument, and response to the response. The result could be a long argument thread.

We define an argument thread is a premise argument followed by a chain of zero or more warrant arguments. The chart below illustrates an single argument thread.

Argument Threads are Dialogs

Argument threads proceed along the lines of “𝐴 because 𝐵, yes but not 𝐶, okay but 𝐷,” and so on. Each argument in the thread is made in the context of all the previous arguments in the thread. The thread may be long, but arguers that are adding to the thread can be assumed to have have followed the whole thread of the argument.

The claims in the thread thus represents a shared context. Each argument in the thread is made in the context of all the previous claims in the thread, and presumes acceptance of all claims but the root claim. For example, when someone argues that ($\text{𝐴◂𝐵◃-𝐶}$) the defendant retracted her confession it is clear from context that they accept (concede) that (𝐵) the defendant signed a confession but still don’t accept that (𝐴) the defendant is guilty.

Now, the arguer may not actually accept 𝐵 to be true, but by responding with a warrant argument instead of a premise argument (e.g. (𝐵◃-𝐺) the signature was forged), they are conceding 𝐵 for the sake of argument, providing a reason to reject 𝐴 even if 𝐵 is accepted.

Considering a longer argument thread, the argument $\text{𝐴◂𝐵◃𝐶◃-𝐷}$ presumes acceptance of 𝐵 and 𝐶: a person who makes this argument is giving 𝐷 as a reason to reject 𝐴 given (even if) 𝐵 and 𝐶 are accepted.

So the warrant of the last argument in the thread can be interpreted as the claim that the premise, given acceptance of all preceding premises in the thread, is a good reason to accept or reject the root conclusion.

Next

Understanding the concepts in this argument model, in particular the difference between premise and warrant arguments, and the idea of argument threads as dialogs with shared context, is critical to understanding the Causal Assumptions in the Distributed Bayesian Reasoning Math.