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Walton schemes

A Walton scheme is a reusable template of argument — a named pattern of premises and conclusion that people actually use to reason.

Walton, Reed, and Macagno catalogued about 60 schemes in their 2008 book. Each scheme also carries a list of critical questions — the standard ways that argument can be challenged. Our argumentation-schemes crate ships instantiable versions of a subset of them.

Example: argument from expert opinion​

Argument from expert opinion
Premises
  • Source E is an expert in domain D containing proposition A.
  • E asserts that A is true.
Conclusion
∴ A is true.

Instantiate it by binding expert, domain, and claim:

use argumentation_schemes::catalog::default_catalog;

let registry = default_catalog();
let scheme = registry.by_key("argument_from_expert_opinion").unwrap();
let instance = scheme.instantiate(&[
    ("expert".into(), "Dr. Vance".into()),
    ("domain".into(), "structural engineering".into()),
    ("claim".into(), "the bridge is unsafe".into()),
].into_iter().collect()).unwrap();

Other schemes​

Walton's catalogue is large; a few names you may recognize:

  • Argument from analogy — "A and B are similar in respects X, Y, Z; A has property P; therefore B probably has P."
  • Argument from cause to effect — "C generally causes E; C happened; therefore E."
  • Slippery slope — "A leads to B, B leads to C, …, therefore A leads to something bad."
  • Ad hominem — "E says A; E has property X; therefore A is suspect."
  • Practical reasoning — "I want goal G; action M achieves G; therefore I should do M."

For the MVP we focus on expert opinion because it underpins most of the scene examples in this site. The other schemes ship in argumentation-schemes::catalog::default_catalog() — instantiate them by key and inspect their premises and critical questions programmatically.

Critical questions as attack templates​

When a responder rejects an assertion, they often do so by picking a critical question. "Expert says the bridge is unsafe" is defeated by any of:

  • Field: Dr. Vance is a civil engineer, but this bridge is suspension — different discipline. → undermines premise 1.
  • Consistency: The other six structural consultants said the bridge was safe. → rebuts the conclusion.
  • Trustworthiness: Dr. Vance was paid by the bridge's demolition contractor. → rebuts via source.

In our encounter bridge, rejection in StateAcceptanceEval corresponds to "the responder has put forward an argument that (credulously) attacks the proposer's." Critical questions are the template for those attacks. See the encounter integration page for the wiring.

In our library​

Further reading​