One major issue for all thinkers and spiritual practitioners is how to know whether the teachings they are following are true and valid and whether their understanding of them is correct. The study of validity, which developed out of the works of Dignaga and Dharmakirti, gives them the necessary tools to determine this for themselves. This book presents the first chapter of the Seventh Karmapa Chdrak Gyatso's Ocean of Literature on Logic- which he composed entirely from memory while sitting in meditation without referring to any texts- along with the work it explains, the first chapter of Dharmakirti's Commentary on Validity. Together, these works explain what it means for our knowledge to be valid and why the Buddha is an authority we can trust. Along the way, it also explains many other issues of relevance to any practitioner, among them whether there is a creator god, why we should meditate on compassion, and the natures of the four noble truths. In particular, this chapter is renowned for its seminal explanation of the proof of rebirth. This makes it an indispensable text for anyone who wants to deepen their understanding and challenge their own beliefs to see whether they are valid or not. In India and Tibet, the works on validity formed one of the five great topics of Buddhism. This book presents one of the most important aspects of that topic in a clear and accessible translation. It will form an essential part of the studies for any scholar or practitioner of Mahayana and Tibetan Buddhism.