Although the development of reasoning is recognized as an important goal of science instruction, its nature remains somewhat of a mystery. This article discusses two key questions: Does formal thought constitute a structured whole? And what role does propositional logic play in advanced reasoning? Aspects of a model of advanced reasoning are presented in which hypothesis generation and testing are viewed as central processes in intellectual development. It is argued that a number of important advanced reasoning schemata are linked by these processes and should be made a part of science instruction designed to improve students' reasoning abilities.
Concerning students' development and use of formal reasoning, Linn (1982) calls for research into practical issues such as the roles of task-specific knowledge and individual differences in performance, roles not emphasized by Piaget in his theory and research. From a science teacher's point of view, this is good advice. Accordingly, this article will expand upon some of the issues raised by Linn in a discussion of the nature of advanced reasoning which attempts to reconcile the apparent contradiction between students' differential use of advanced reasoning schemata in varying contexts with the notion of a general stage of formal thought. Two key questions will be discussed: Does formal thought constitute a structured whole? And what role does propositional logic play in advanced reasoning? The underlying assumption of the present discussion is that, among other things, science instruction should concern itself with the improvement of students' reasoning abilities (cf. Arons, 1976; Arons & Karplus, 1976; Bady, 1979; Bauman, 1976; Educational Policies Commission, 1966; Herron, 1978; Karplus, 1979; Kohlberg & Mayer, 1972; Moshman & Thompson, 1981; Lawson, 1979; Levine & linn, 1977; Pallrand, 1977; Renner & Lawson, 1973; Sayre & Ball, 1975; Schneider & Renner, 1980; Wollman, 1978). The questions are of interest because to date they lack clear answers, yet clear answers are necessary if we hope to design effective instruction in reasoning.