Structural Determinants of Counterfactual Reasoning

Structural Determinants of Counterfactual Reasoning Daniel Yarlett (dany@cogsci.ed.ac.uk) School of Cognitive Science, University of Edinburgh 2 Buccleuch Place, Edinburgh EH8 9LW Scotland Michael Ramscar (michael@dai.ed.ac.uk) School of Cognitive Science, University of Edinburgh 2 Buccleuch Place, Edinburgh EH8 9LW Scotland Abstract In this paper we explore the hypothesis that the processes un- derlying the matching and use of knowledge during counter- factual reasoning are the same as those that underlie reasoning by analogy. We report two experiments which indicate that, in common with analogical reasoning, counterfactual reason- ing exhibits the following properties: (i) it is sensitive to sys- tematic structural congruencies between representations; (ii) when background knowledge has to be retrieved before it can be exploited, the impact of structurally congruent background knowledge on the counterfactual inferencing process is medi- ated by featural commonalities. Introduction If it had not been for a young student at the University of Chicago in 1960, the Cuban missile crisis might have es- calated to a nuclear war. At first blush this counterfactual sounds absurd, a non sequitur – how can there possibly be a link between a single student and the avoidance of nuclear war? It turns out, though, that the assertion isn’t quite as far fetched as one might initially think: “Not yet twenty-one and too young to vote, the student worked in the Kennedy campaign. He was asked by the local Democratic organization if he would vote on be- half of a dead voter whose name was still on the rolls. He readily agreed and, refusing the small remuneration that was offered, forged the dead voter’s signature and voted a straight Democratic ticket. The Illinois vote was close – Kennedy took the state by fewer than 10,000 votes – and critical. Illinois gave Kennedy the neces- sary electoral votes to win the presidency. ” (Lebow and Stein, 1996, p.119). This additional knowledge connecting the student’s actions to Kennedy’s electoral success allows the rest of the story to fall into place. Had the student – and, crucially, others like him – not forged votes, Nixon may have been elected instead of Kennedy; if Nixon had been elected he would have estab- lished a much less liberal administration; a less liberal ad- ministration would have responded more forcefully to Khr- uschev’s deployment of missiles in Cuba; and the odds are that this would have led to further military escalation and, ultimately, nuclear war. This is not a watertight argument of course – the strength of some of the links in the argumentative chain is question- able – but it does serve to make apparent the relation between the two events which at first appeared utterly disparate. 1 And understanding that there is a connection between the exis- tence of a group of students and the avoidance of nuclear war makes the initial counterfactual seem much more plau- sible than it did before: if those students hadn’t existed then we can now see that this might just have tipped the balance in the favour of nuclear war. Background knowledge is clearly crucial to our assessment of counterfactuals, then, but how it is matched and used during counterfactual reasoning? In this paper we explore the possibility that the pro- cesses underlying the matching and use of knowledge dur- ing counterfactual reasoning are the same as those that un- derlie reasoning by analogy. Although there has been exten- sive research into counterfactual reasoning over the last two decades from a cognitive-functional perspective (for repre- sentative overviews see Roese, 1997; Kahneman & Miller, 1986; Byrne & Tasso, 1999), no-one has explicitly inves- tigated the effect of structural congruency on the inferenc- ing process. We report two novel findings in support of the hypothesis that analogical mechanisms do underpin counter- factual reasoning in at least some contexts. In Experiment 1 we show that an analogical match be- tween background knowledge and a scenario about which subjects have to reason counterfactually significantly boosts their assessments of the soundness of related counterfactual inferences. This suggests that when engaged in counterfac- tual reasoning subjects rely on systematic structural matches between representations just as they do when making ana- logical inferences (Gentner, 1983; Holyoak and Thagard, 1995). Furthermore, previous studies in analogical infer- ence and problem solving have found that it is difficult to ex- ploit the information contained in analogies during real-life problem-solving because analogies are typically difficult to retrieve (Gick and Holyoak, 1980; Gentner, Ratterman and Forbus, 1993). In Experiment 2 we add a retrieval require- ment to the task investigated in Experiment 1, and show that this same finding also applies to counterfactual reasoning. Why Analogy? Theories of counterfactual reasoning agree that similarity plays a core role in determining legitimate inferences – in order to evaluate what would be true if A were the case, it makes sense to consider only the state of affairs that is most similar to the way things actually are, except that in 1 See Lebow and Stein (1996) for a fuller analysis of the plausi- bility of this counterfactual sequence of events.