Unless Reasoning

Article excerpt

We report the results of two experiments investigating conditional inferences from conditional unless assertions, such as Juan is not in León unless Nuria is in Madrid. Experiments 1 and 2 check Fillenbaum's hypothesis about the semantic similarity of unless with if not and only if assertions; both also examine inferential endorsements (Experiment 1) and endorsements and latencies (Experiment 2) of the four logically equivalent conditional formulations: if A then B, if not-B then not-A, A only if B and not- A unless B. The results of these experiments show the similarity of unless and only if, confirming that the representation of both conditionals from the outset probably include two possibilities directionally oriented from B to A; results also confirm the especial difficulty of unless assertions. The implications of the results are discussed in the context of recent psychological and linguistic theories of the meaning of unless.

Keywords: conditionals, propositional reasoning, mental models

Se presentan los resultados de dos experimentos que investigan las inferencias a partir de enunciados condicionales a menos que, tales como "Juan no está en León a menos que Nuria esté en Madrid". Los experimentos 1 y 2 comprueban la hipótesis de Fillenbaum sobre la similaridad semántica de los enunciados a menos que con si no y sólo si; ambos experimentos examinan las respuestas inferenciales (Experimento 1) y las respuestas inferenciales y las latencias (Experimento 2) de las cuatro formulaciones condicionales lógicamente equivalentes: si A entonces B, si no-B entonces no-A, A sólo si B y no-A a menos que B. Los resultados muestran la similaridad de a menos que y sólo si, confirmando que la representación de ambos condicionales probablemente incluya desde el principio dos posibilidades orientadas direccionalmente desde B a A; los resultados también confirman la dificultad especial de las afirmaciones del tipo a menos que. Las implicaciones de los resultados se comentan en el contexto de las teorías psicológicas y lingüísticas sobre el significado de a menos que.

Palabras clave: condicionales, razonamiento proposicional, modelos mentales

Our aim is to examine some linguistic and psychological hypotheses about the meaning of unless conditionals by using conditional inference tasks. First, we outline a mental model theory of conditional reasoning and consider the possibilities people keep in mind to understand if then and if not then conditionals; we suggest that they represent only one of the possibilities from the outset to understand if then and if not then. Second, we examine the possibilities they think about in understanding only if conditionals and suggest that they represent two of the possibilities from the outset to understand them. Third, we review linguistic and psychological theories and evidence regarding unless and consider the possibilities people think about to understand this connective. We report two experiments that compare unless with if then, if not then and only if.

During the last four decades a great deal of psychological research has been devoted to propositional reasoning, particularly to conditionals. The study of how people reason from conditional statements has become the main concern of research in deductive reasoning (see, Evans, Newstead, & Byrne, 1993). Four main theoretical approaches have been posited in propositional reasoning. Mental rules theories claim that the reasoning process is based on the application of formal rules of inference (e.g., Braine & O'Brien, 1998; Rips, 1994). There is also a view claiming that conditional reasoning is based on domain-specific rules of inference (e.g., Fiddick, Cosmides, & Tooby, 2000; Holyoak & Cheng, 1995). The third approach, mental model theories, maintains that reasoning processes rely on the ability to imagine possibilities (e.g., Johnson-Laird & Byrne, 1991; Johnson-Laird & Byrne, 2002; see also Evans, 1993). …