The Causal Nexus is a highly relevant theme for Law: Civil or Criminal. However, one must have its real notion and origin, which came from Philosophy and Physics. For this, the study goes into the concepts of Philosophy and Physics to clarify its notions and actuality in Modern Physics and in a perception of Philosophy integrating Will and Action. Alongside this, the interpolations of other wills and actions in its course and effects. The notion of Lide by Professor Galeno Lacerda and Obligation as Process by Professor Clóvis do Couto e Silva stand out.