Abstract: In order to be considered a vice of consent, the error must have, among other conditions, an essential character. This condition consists in that the false representation of reality within the consciousness of one of the parties of the contract must cover the essential elements for  concluding the act. The assessment of the determinative character of the  error is done according both to objective criteria, established by law, and also to  subjective criteria, indicated within the contract by the parties. Among the objective elements can be mentioned: the nature or the object of the contract, the identity of the object of the contract, the quality of the object of the obligation, the identity or the quality of the contractual partner, the existence or the content of a legal rule. The subjective elements are called the determinant reasons and refer to any circumstance in the consideration of which the    party in error gave its consent, provided that it has been referred to by contract. In the case of bilateral acts for pecuniary interest it is required that the cocontractor is aware of the essential character of the element upon which the error bears. If the error is insignificant or indifferent, the party which invokes it can not request the  annulment of the act, but only payment of damages.

Keywords: essential error, determinative element, object of the contract, identity of the contracting party, decisive reasons