Abstract
Concerned with the analysis of the good faith concept, as flexible concept, there are some people who have considered that law compels the judge to look at good faith and justice and usually to reconsider the contractual background in order to discover new commitment susceptible of variations and multiplications during time. In the circumstances that, good faith is an instrument of interpreting contracts, and the judge wonders what it is that the parties, of good faith, could have desired to hire, we understand here the demands of a behavior rule in performing the convention.