Short answer. It has no effect. Article 1183 of the Civil Code states that a condition not to do an impossible thing shall be considered as not having been agreed upon. The condition is simply struck out of the contract and the rest of the obligation stands as if that clause was never written.
What the law says
The condition not to do an impossible thing shall be considered as not having been agreed upon.
Civil Code, Article 1183 — Impossible and Unlawful Conditions. Read the full provision →
Two opposite rules for impossible conditions
Article 1183 treats impossible conditions differently depending on how they are phrased. A condition that requires you to do something impossible annuls the obligation that depends on it — the whole arrangement is void because its trigger can never happen. But a condition that requires you not to do something impossible is handled differently: it is simply ignored. The law considers it as if you and the other party never wrote it. This distinction is not arbitrary; it reflects the practical reality that a prohibition on something impossible places no real burden on anyone.
Why a negative impossible condition is disregarded
If you promise not to fly to the moon under your own power, that promise costs you nothing and restricts nothing. The condition is always automatically satisfied — you will never breach it because the act is beyond human capacity. Treating it as voiding the obligation would let either party escape a contract simply by inserting a meaningless clause. The Civil Code avoids this outcome by declaring the clause considered as not having been agreed upon. The obligation continues on its own terms without that condition.
How this differs from an affirmative impossible condition
The contrast matters in practice. If the contract required you to perform an impossible act as a condition of your obligation — say, to deliver a commodity that no longer exists anywhere — the obligation dependent on that condition is annulled. Neither side can enforce it. The logic is the reverse: if the condition can never occur, the obligation can never arise, and the creditor can never claim. So whether impossibility voids the obligation or just eliminates the condition depends entirely on which direction the impossible act was framed.
Practical takeaway
If your contract contains a clause saying you must refrain from something that nobody could do anyway, you can set it aside. It does not affect your other obligations under the contract. The clause does not give the other party leverage against you, and you do not need to take any action to remove it — the law already treats it as unwritten. Where the analysis becomes less clear is if the 'impossible' act is debatable, or if the clause was included to define the scope of a broader restriction. In those cases, how a court will characterize the condition depends on the full context of the agreement.
Cases citing this provision
These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.
- Heirs of Severina San Miguel, et al. vs. The Hon. Court of Appeals, G.R. No. 136054, September 5, 2001 — read the decision on LawPhil →