The literature on certainty in law occupies an entire library. A particularly important place is reserved for Humberto ?vila’s book in this vast imaginary library. While presenting itself as a work of jurisprudence on the Brazilian Constitution (and specifically on Brazilian tax law, a field in which the author is an acknowledged expert), this book undoubtedly has a far broader theoretical scope. Moreover, it is probably the most comprehensive and systematic study ever produced on this subject using the analytical method. Professor ?vila deconstructs certainty in law, reducing it to its constituent elements and showing all its multiple dimensions, both conceptual and institutional. 1. The concept of legal certainty. In the prevailing legal doctrine and theoretical tradition, which dates from the Enlightenment and is rooted in legal positivism, law is certain if and only if everyone can accurately foresee the legal consequences of their own actions and know ex ante the limits of the state’s coercive powers and how they are exercised. ?vila elaborates a far more articulate concept of legal certainty in a moderately “realist” theoretical context as far as interpretation is concerned.