Logic is the discipline which studies reasoning. Logic has its roots in our argumentative practice,and was developed as a tool for the critical description and evaluation of natural languagearguments. These origins stand in sharp contrast with the received view of formal, symbolic logicas a mathematical enterprise leading us from true premises to true conclusions.In our practice of deciding how to act in the presence of intentions, norms, and beliefs, we oftenmake inferences which lead us from true premises to conclusions which are highly plausible andrationally compelling, but not necessarily true. These inferences are defeasible: their conclusion isdrawn tentatively, subject to retraction in the light of additional information. We often reasondefeasibly, and so should we. It is important that we do not simply dismiss such inferences aslogical fallacies, but that we recognize their importance, and that we study them in their own right.The aim of this project is to study our argumentative practice with appropriate formal tools whichstem from the theory of formal argumentation in the field of artificial intelligence. On the onehand, these tools, like modern-day symbolic logic, provide us with the means for explicating andevaluating our argumentative practice in an exact, precise manner. On the other hand, they arecapable of capturing defeasible aspects of our argumentative practice.