Based on a comparative evaluation of the case law of the Constitutional Courts of Peru and Chile on implied fundamental rights, this work evidences some strengths and weaknesses of the foundation and determination of these rights. The aim of this work is to introduce an alternative account for the understanding of implied fundamental rights. This alternative account does not deny the dual nature of law held by Alexy's non-positivism, but it goes further and it can be identified as a “Moderate Natural Law Theory” approach of those rights.