Does the Law exist? and if so, what is it? Can we know it? This book tries to answer these questions by approaching as a whole the problem of Law, its justification and demonstration. Because when facing multiple legal theories, many of which are contradictory, we have to ask ourselves what the true Law is, if it exists indeed, its origin, meaning and perspective. We are in pursuit of something more: the Law and its truth. This fundamental question must be scientifically solved, and in such an in-depth approach that only philosophy, traditionally understood as "knowledge by its first and principle causes, obtained under the natural light of reason," can give us the answer. the current thesis takes up the problem of knowledge and its theories of being and truth, to later contrast them with various juridical currents. Two different paths, processes and objects to reach the same conclusion. the result wasn't easy, but we believe we contributed with a juridical theory with seven rules of truthfulness, that from our humble point of view, solves the conflict over Law, its essence and properties. What is Right? What is Law? Does a juridical science exist? Does a true theory of Law exist or does each one of us have their own truth? These were the central questions we tried to answer in the current thesis; to demonstrate through reason the considerations raised here and to somehow contribute in a positive way to the growing relativism of this subject.