Contrary to the assertions of a certain type of legal realism, this paper seeks to demonstrate that - at least in some of the cases in which the law is indetermined - the legal and not the political reasons, are the best to explain judicial decisions. In order to do so, first, the thesis of the indeterminacy of law is examined, distinguishing between its various aspects, and differentiating it from the disagreements. Then, the sense the legal reasons explain the cases in which the law is determined is explained. Subsequently, it is argued that, at least sometimes, legal reasons are the best to explain the judicial decisions when law is indeterminate. Finally, interdisciplinary nature to explain, and forecast, judicial decisions is advocated.