This book, now in its second edition, offers original answers to all the major open questions in epistemology-as indicated by the book's title. These questions and answers arise organically in the course of a validation of the entire corpus of human knowledge. The book explains how we know what we know, and how well we know it. The author presents a positive theory, motivated and directed at every step not by a need to reply to skeptics or subjectivists, but by the need of a rational individual to know the world. The author draws heavily from Ayn Rand's theory of concepts as presented in her book, Introduction to Objectivist Epistemology, but departs from her epistemology-especially as explicated by leading exponents of her philosophy-in important ways. Areas of departure include the perception of entities and the role of probability theory in epistemology. A main idea in the book is to begin the validation of the law of causality by identifying that existence causes our consciousness of it. Another key idea is this: The very fact that we perceive entities is the most basic and most extensive evidence that causal forces and causal interactions are regular. This book is primarily for a specialized readership-familiar with epistemological ideas and with Ayn Rand's theory of concepts in particular. The last third of the book uses probability theory and mathematics somewhat beyond basic calculus, but less mathematical explanations are also included to make the general ideas accessible to lay readers.