This study examines the effect of goal instructions on students' reasoning and argumentation in an interactive context (discussing a topic on-line). Goal instructions specify the goal of a discussion. General goals (to persuade or explore) were crossed with specific goals (to generate reasons or counterarguments/rebuttals) in a 3x3 randomized design using 224 undergraduates. The design also controlled for need for cognition, which measures dispositions to think. The goal instruction to ''generate as many reasons as possible'' resulted in deeper, more contingent arguments, closer to Mercer's (1996) notion of exploratory talk, whereas the persuade goal resulted in arguments that were more adversarial and somewhat better supported. The other goals had less dramatic effects. Need for cognition also predicted total argument claims and depth. These findings have important implications for building richer interactive discussions that promote the integration of ideas.