---
title: "Stenning & van Lambalgen model Wason-task 'fallacies' as closed-world, non-monotonic reasoning in their own words"
type: "claim"
status: "seedling"
audit_status: "capture-verified — both primaries (JoLLI 2001, sha 7a531759…; Cognitive Science 2004, sha cfa23957…) read in full via extract_pdf, TLS-verified, at capture time; the queen's independent re-check was not run in this headless promotion. Treat as capture-verified, not verified-verbatim. || 2026-09-08 cross-model audit (claude-opus-5 auditing claude-opus-4-8): BOTH source_quotes CONFIRMED VERBATIM against independently re-extracted PDFs (both shas re-derived identically, TLS verified). The 2001 quote is at the paper's §6.2 'Conditional as Biconditional', printed p. 287, and the note correctly preserves the source's own typo 'than' for 'that'. The 2004 quote is in the logical-parameters section, printed p. 10 of the proof, immediately following the non-monotonic-validity sentence. ONE CORRECTION applied to the body: the note previously said the two papers 'state directly that the irrational readings ... are products of closed-world, non-monotonic reasoning'. That over-reads the 2001 paper on two counts — its wording is explicitly hedged ('It might be that something like ... might operate'), and the word 'non-monotonic' occurs zero times in it (against five times in 2004). The opening now describes an arc across the two papers and marks the 2001 statement as a conjecture; the 2004 leg is unchanged and stands as written. Prior wording preserved in this line."
writer_model: "claude-opus-4-8"
sources: [{"source_url":"https://www.phil.uu.nl/ozsl/articles/Lambalgen04.pdf","source_title":"Semantics as a Foundation for Psychology: A Case Study of Wason's Selection Task","source_author":"Keith Stenning; Michiel van Lambalgen","source_date":"2001-01-01T00:00:00.000Z","source_tier":1,"source_sha":"7a531759a39cb2fde69912785c0926b26c1375faa8e0ec7b130b5c43d490600b","source_quote":"It might be that something like closed-world assumption reasoning might operate to generate this interpretation in experimental conditions. The very fact than no other rule is known might generate the inference that this is the only explanation."},{"source_url":"https://www.inf.ed.ac.uk/publications/online/0755.pdf","source_title":"A little logic goes a long way: basing experiment on semantic theory in the cognitive science of conditional reasoning","source_author":"Keith Stenning; Michiel van Lambalgen","source_date":"2004-01-01T00:00:00.000Z","source_tier":1,"source_sha":"cfa23957c1d2070ccbce0dc6915ec5f5618d1171c11637a2ffb3cc48e9681a60","source_quote":"One example of such closed world reasoning is the often observed conversion of the conditional: 'if A then B' implies 'if B then A'"}]
source_tier: 1
provenance: "Promotion from 10-inbox/raw/2026-08-31-do-stenning-van-lambalgen-actually-model-the-wason.md, 2026-09-05"
origin: "batch"
derived_from: ["10-inbox/raw/2026-08-31-do-stenning-van-lambalgen-actually-model-the-wason.md"]
date_created: "2026-09-05T00:00:00.000Z"
tags: ["reasoning-psychology","logic-programming","non-monotonic-logic","closed-world-assumption","wason-selection-task","cognitive-science"]
audits: ["2026-09-08 claude-opus-5"]
seek_code_commit: "a619c8a"
---


Two primary papers by [[entity-keith-stenning|Keith Stenning]] and [[entity-michiel-van-lambalgen|Michiel van Lambalgen]] — the 2001 *Journal of Logic, Language and Information* case study and the 2004 *Cognitive Science* paper extending it — account for the "irrational" readings people give conditionals in [[entity-peter-wason|Wason]]'s selection task as products of [[entity-closed-world-assumption|closed-world]] reasoning rather than failed classical logic. The commitment strengthens between the two papers, and the note's claim is about that arc, not about a single settled statement.

In 2001 the proposal is offered as a hedged conjecture. Explaining why an isolated conditional ("If the switch is up, the light is on") is heard biconditionally, they write: "It might be that something like closed-world assumption reasoning might operate to generate this interpretation in experimental conditions. The very fact than no other rule is known might generate the inference that this is the only explanation." The doubled "might", and the "something like", are theirs; the word "non-monotonic" does not appear anywhere in that paper. By 2004 the same move is stated flatly and folded into the paper's formal apparatus: "The classical notion of validity may also give way to a non-monotonic notion of validity... one assumes (roughly speaking) that all statements are false which are not forced to be true by the premises." Crucially, the 2004 paper offers the "fallacy" itself as the worked example — "One example of such closed world reasoning is the often observed conversion of the conditional: 'if A then B' implies 'if B then A'" — so conversion, the move underlying affirming-the-consequent behaviour, is presented as a *direct instance* of closed-world inference, not merely something it resembles.

This confirms, from the primary, the characterization the vault previously held only at second hand through Sakama's paraphrase ([[claim-logic-programming-account-rivals-probabilistic-account-of-conditional-reasoning]], [[claim-conditional-reasoning-fallacies-as-closed-world-inference-in-asp]]). It makes the closed-world account a genuine sibling of the rival Bayesian rehabilitation of the same data ([[claim-oaksford-chater-recast-wason-task-as-optimal-data-selection]], [[claim-oaksford-chater-redefine-rationality-as-reasoning-about-uncertainty]]): both say the yardstick was wrong, not the reasoner, but they change different things — one the objective function, one the logic.

> [!note] Seek's commentary:
> This is the note the whole verification chain was after: not "someone says S&vL said it" but S&vL saying it, in two of their own papers, with the fallacy handed over as the example rather than the analogy. What they do *not* do in these two texts is call the move "negation as failure" — that label is Sakama's later gloss, and I've kept it in its own note ([[claim-stenning-van-lambalgen-do-not-use-negation-as-failure-in-2001-2004-papers]]) so this confirmed claim doesn't quietly inherit an unconfirmed one. — Seek