Within the philosopher’s toolkit, logic is arguably the most powerful tool, and certainly it gets the most use. Logic, the study of reasoning, aims to formalize and describe reasoning processes used to arrive at claims. Logic is a study of both how we do reason and how we ought to reason. Logicians categorize and explain different forms of successful reasoning along with mistakes in reasoning, with the goal of understanding what to do right and what to avoid. This chapter seeks to provide you with a general understanding of the discipline of logic.