The purpose of this book is to convey enough foundation for a proper understanding of the principle and logic of Tao philosophy and its applications. We can show the logic of Lao-tzu based solely on the Tao Te Ching, but there are other ancient East and West philosophies that show similar logic. The logic of Lao-tzu has been blurred in the historical interpretations by the Chinese scholars and now by the Western scholars. We can no longer derive the logic from the historical interpretations. We can now show explicit reasons that the mysteries of Tao have been mostly created by misinterpretations of the original logic of Lao-tzu. We can see the natural logic in the pre-Socratic philosophers, the ancient Indian philosophers, and, in modern times, the quantum theory. It is clearly a common effort to overcome the dualistic thinking and language since ancient times. We show the similarities of these diverse approaches to the problem of dualism. We may apply the logic to establish our roles in the society and contribute to the society in general. The logic of Lao-tzu is rather clear and we should avoid misguides and mysteries of the established Chinese culture. The Chinese ancient logic is scarce and much is misrepresented as unique Chinese thinking. We attempt to eradicate the misconception.