Conditional (if-then) reasoning occupies a central place in the study of logical reasoning. Reasoning with conditionals is a part of everyday thinking (e.g. Scholnick & Wing, 1991) and is important to activities such as reading (Lea et al., 1990). In addition, the ability to make ‘if-then’ inferences that are hypothetical and logical underlies much of formal mathematics and underpins many of the physical sciences. Understanding the nature and the corresponding developmental trajectory of conditional reasoning abilities is thus crucial to the basic understanding of the nature of logical reasoning. This is also important for very practical reasons, since promoting the ability to reason logically must be an important educational goal.

Conditional reasoning is one of the key components of a system of logical norms referred to as propositional logic. Although modern logic acknowledges the existence of different forms of logic, there is an intuitive presumption that standard propositional logic constitutes a template for logical reasoning. This can be seen in textbooks that teach logic and reasoning, where propositional logic is an explicit or implicit model for good reasoning. There is also a clear link between the idea that standard propositional logic is the norm for good reasoning and psychological theories of the nature and development of reasoning abilities. This can be seen most clearly in two important theories that share a common biological theme.