A study investigated the relationship between formal and conversational logic. Thirty-two male and 32 female college students evaluated the conclusions of conditional syllogism and participated in an interview adapted from Deanna Kuhn's (1991) monograph, "The Skills of Argument." Students were asked to provide explanations for several problems of interest to them, such as drinking problems, pregnancy, and college tuition. After providing a theory, students were asked to imagine the proof that would support it, and to specify the kinds of evidence that would refute their theory. Then they were offered an alternative theory, which they were to try to refute and then do the opposite--describe the evidence that would support it. Results supported the premise that reasoning in discourse is the same type of reasoning people employ in logical tasks if given the opportunity. But while the data show a relation between two contexts in mature reasoners, they do not illuminate the nature of the relation nor its developmental course. There three possibilities: (1) that both conversational reasoning and formal logic reflect the development of logical skills that are present prior to the advent of language and which will continue to develop; (2) that language plays a constitutive role with the emergence of conditional reasoning; and (3) that language and formal logic are mutually constitutive. The meanings language conveys enable representation of the premises, and the syntax enables coordination. Contains 13 references. (AA)