Short answer. No. Under Article 873 of the Civil Code, conditions attached to a legacy that are contrary to law are treated as if they were never written. The condition is simply disregarded, and you receive the legacy unconditionally — even if the testator expressly tried to make it conditional.
What the law says
Impossible conditions and those contrary to law or good customs shall be considered as not imposed and shall in no manner prejudice the heir, even if the testator should otherwise provide.
Civil Code, Article 873 — Impossible and Unlawful Conditions. Read the full provision →
The condition disappears, not the legacy
Article 873 of the Civil Code draws a clear line between the condition and the gift itself. When a testator attaches an impossible condition, or one that is contrary to law or good customs, the law treats that condition as if it were never part of the will. The legacy or devise is not cancelled — only the offending condition is stripped away. The result is that you receive the legacy as a pure, unconditional gift. The testator cannot change this outcome even by specifically trying: the article adds that the rule applies even if the testator should otherwise provide.
Three kinds of conditions the law neutralizes
Article 873 covers three overlapping categories. First, impossible conditions — those that literally cannot be fulfilled because they require something physically or logically beyond reach. Second, conditions contrary to law — those that would require the heir to commit an illegal act, violate a statutory prohibition, or disregard a legal duty. Third, conditions contrary to good customs — those that are not necessarily illegal but offend accepted moral standards. All three are treated identically: considered not imposed, with no effect on the heir's entitlement.
Why the law takes this position
Testators have wide freedom to dispose of their estate as they see fit, but that freedom has limits. One limit is that the state will not enforce conditions that require someone to break the law or abandon morality in order to inherit. Doing so would mean using inheritance law as a vehicle for pressuring people into unlawful conduct. By declaring such conditions void while preserving the bequest itself, the law respects the testator's wish to benefit the heir while refusing to give legal force to a coercive or illegal demand attached to that gift.
What you should do if this applies to your situation
If you are facing a will that conditions a legacy on something you believe is unlawful or impossible, you do not need to comply with the condition to claim what was left to you. However, other heirs or co-legatees may dispute the characterization of the condition, and there may be a formal probate proceeding where the question needs to be raised. Presenting the issue clearly and at the right time — during probate, not after distribution — is important. A lawyer familiar with probate proceedings can help you frame the argument and protect your share.