The co-ordination between theory and evidence is an outstanding characteristic of scien¬tific thinking. Research indicates that students often have difficulty in explaining natural phenomena because they use their own theories to explain phenomena or they are unable to build a bridge between theory and evidence. Science teachers must teach students to collect and select evidence and to use theory to explain it. The objective of this study was to investigate the forms of reasoning used by prospective physical sciences teachers when they build up explanations and make predictions about natural phenom¬ena. Thirty-eight prospective teachers answered a questionnaire structured around three problems focus¬ing on phenomena that can be explained th...