ABSTRACT
This chapter presents at a debate where one debater accused the other of cheating by using reasoning. Tree diagrams, diagrams in which the critical information is represented along 'branches', like a tree, can be used to determine validity with if, then deductive reasoning problems. As with all of the forms of deductive reasoning that are covered in the chapter, the content of the premises and our own belief biases influence the way we determine what sorts of conclusions we are willing to accept as valid. The skills presented in the chapter are used to determine if a conclusion is valid, that is, it must be true if the premises are true. These skills are used in many contexts including law, medicine, financial projections, and the sciences. The ability to reason well is a critical thinking skill that is crucial in science, mathematics, law, forecasting, diagnosing, and just about every other context you can imagine.
