JOURNAL OF EXPERIMENTAL CHILD PSYCHOLOGY 48, 90-113 (1989) Reasoning about Conditional Sentences: Development of Understanding of Cues to Quantification DAVID P. O’BRIEN Baruch College of the City University of New York AND MARTIN D. S. BRAINE, JEFFREY W. CONNELL, IRA A. NOVECK, SHALOM M. FISCH. AND ELIZABETH FUN New York University The previous literature has reported that when children are asked to judge the truth or falsity of universally quantified conditional sentences of the form If a thing is P then it is Q they typically give erroneous responses, e.g., responding “true” whenever there is a case of P and Q even if there are also cases of P and not-Q. Three experiments are reported that address possible sources of this error. Experiment 1 shows that the error survives on sentences that refer to particular things as well as to things of a particular kind, and further shows that articulating the necessity of the consequent (. then it has to be Q) eliminates the error for adults and reduces it for fifth graders, although it does not affect second grade performance. Experiment 2 shows that for second and fifth graders the error survives to problems that are not universally quantified and for second graders to problems that are not conditionals although are otherwise structurally similar. Experiment 3 compares various verbal formulations of such universally quantified conditionals: Second and fifth graders do not make the error when the quantification is expressed with the surface structure that makes its universality most explicit (all things . .); the error tendency is greatest when the indefinite article is used (if a thing . .); and formulations using any fall in between. We argue that such erroneous evaluations of universally quantified conditionals have more to do with the quantificational aspect than the conditional aspect of the problems; children interpret the indefinite article as existential, although they This work was supported by a grant from the PSC-CUNY research award program of the City University of New York to David O’Brien, and by an NSF grant (BNS-8409252), Martin Braine. principal investigator. The authors thank the students, teachers. and prin- cipals of PS 3 in Manhattan and the Flushing Christian Day School and the Our Lady of Senacle School in Flushing, Queens. Requests for reprints should be sent to David O’Brien, Department of Psychology, Baruch College of the City University of New York, Box 512. 17 Lexington Avenue. New York, NY 10010. 90 0022~0965/89 $3 .OO Copyright 0 1989 by Academic Press, Inc. All rights of reproduction in any form reserved