This document aims to contrast the right of preference in the sell of shares and the usufruct of shares, as two legal figures accepted by the Colombian legal system, to explain how they can bring about an illicit cause for contract and result in a atypical illicit act. In order to develop purpose, in the first place, the article will present generalities of “atypical illicit”. In second place, it examines matters related to the cause of the acts or contracts, the nullity resulting from an illicit cause, and finally, the theory of atypical illicit act applied to the issues initially raised by the two figures considered above.
