Short answer. Four requisites under Article 1437 of the Civil Code: fraudulent representation or wrongful concealment of facts known to the person estopped, that person's intent that the other act on the misrepresented facts, the misled party's genuine unawareness of the truth, and that the misled party actually acted in accordance with the misrepresentation.
What the law says
There must be fraudulent representation or wrongful concealment of facts known to the party estopped; (2) The party precluded must intend that the other should act upon the facts as misrepresented; (3) The party misled must have been unaware of the true facts; and (4) The party defrauded must have acted in accordance with the misrepresentation.
Civil Code, Article 1437 — Estoppel in Land Transactions. Read the full provision →
The rule this estoppel is built on
Article 1437 addresses a specific scenario: in a contract between third persons concerning immovable property, one of them is misled by a person with respect to ownership or a real right over the real estate. Where that happens, the person responsible for the misleading is precluded, meaning legally barred, from later asserting his own legal title or interest in that property against the person he misled. This prevents someone from creating a false impression about land ownership and then reversing course once it benefits him to assert the truth.
The first two requisites: representation and intent
Article 1437 requires, first, fraudulent representation or wrongful concealment of facts known to the party estopped, meaning the person did not merely make an innocent mistake but either actively misrepresented the facts or wrongfully hid facts he actually knew. Second, the party precluded must intend that the other should act upon the facts as misrepresented, meaning the misrepresentation was not incidental but was meant to influence the other person's conduct regarding the property in question.
The second two requisites: the misled party's position
The remaining two requisites focus on the person who was misled. The party misled must have been unaware of the true facts, meaning the estoppel does not protect someone who actually knew the truth despite the misrepresentation. And finally, the party defrauded must have acted in accordance with the misrepresentation, meaning there must be an actual connection between the false impression created and what the misled party then did, such as entering into the contract concerning the property.
Why all four requisites matter together
Article 1437 requires that all of these requisites be present, not just some of them. Missing even one, for instance being unable to show the misled party genuinely acted based on the misrepresentation rather than for some independent reason, means the estoppel this article creates does not apply. Establishing a claim under Article 1437 therefore means being able to support each of the four elements with specific facts, not simply showing that a misleading statement was made at some point in the transaction.