To enforce a contract against a third party, the principle of opposability must be complied with. Opposability consists of the possibility of a person to enforce a right against a third party.

For this to be possible, it is necessary that said third party has or may have knowledge of the existence of said right. The way to achieve this is by notarizing it into a public deed, since if it is not done, a third party who evades that right and proves that they acted in good faith would not be liable for such evasion.