The Thinker's Guide to Intellectual Standards details and analyzes the ways by which reasoning is judged in skilled thought. The fundamental goal of this book is to illuminate the importance of explicitly mastering intellectual standards with a view to improving thinking across the multiple domains of human life. This guide provides the foundations for thinking about the role played by standards in human thought, and the need to advance and embrace universal intellectual standards such as clarity, accuracy, relevance, significance, and sufficiency in reasoning through problems and issues. Those proficient in the use of intellectual standards think more effectively in every domain and subject in which, or about which, they think. As part of the Thinker's Guide Library, this book advances the mission of the Foundation for Critical Thinking to promote fairminded critical societies through cultivating essential intellectual abilities and virtues across every field of study across world.