This chapter presents a brief account of theoretical reason, particularly its basis. It addresses the following questions: what are the sources of justified beliefs? How are such beliefs grounded? How does their justification vary from one context to another? How may their justification be defeated by, say, counter-evidence? What is the role of coherence or incoherence in this grounding or defeat? And is such defeat itself based on the same kinds of grounds as the justification it vanquishes?
Keywords: theoretical reason, justification, beliefs, coherence, incoherence