The interpretation of the law allows to recognize the elements that make up the legal reality both for the judge when applying it, as well as for individuals when guiding their conduct. This activity is limited by guidelines or criteria to be followed, which determine the standards to be considered valid. The recent reform of the civil and commercial legislation introduced changes in the regulation of interpretation, modifying the criteria that allow determining the law to be applied. This paper attempts to inquire into the theoretical foundations that justify such modification, in order to analyze and evaluate its practical consequences. To this end, we will try to show the direct relationship between the concept of law, the different philosophical conceptions of law and the guidelines to interpret it.