What is the difference between annulment, declaration of nullity, and legal separation?

Why

A Declaration of Absolute Nullity applies to marriages that are void from the beginning ('ab initio')—the law treats the marriage as having never existed. Common grounds under the Family Code include lack of a marriage license, bigamous or polygamous unions, incestuous marriages, and psychological incapacity under Article 36. Void marriages do not have a prescriptive period and can be challenged at any time.

Annulment applies to voidable marriages—marriages that are considered legally valid until a court sets them aside. The grounds must have existed at the exact time of the wedding under Article 45: lack of parental consent for spouses aged 18 to 21, unsound mind, fraud in obtaining consent, force, intimidation, or undue influence, physical incapacity to consummate (impotence), or a sexually transmissible disease that is serious and appears incurable. Most annulment grounds must be raised within five years under Article 47 (counted, depending on the ground, from turning 21, from discovering the fraud, from the time the force ceased, or from the wedding), and the first four grounds can be cured if the injured spouse later freely cohabits with the other with full knowledge.

Legal separation is fundamentally different. The marriage bond is not severed, and neither spouse may remarry anyone else. A decree of legal separation merely entitles the spouses to live separately from bed and board, dissolves and liquidates the absolute community or conjugal property (the guilty spouse forfeits his or her share of the net profits), awards custody of minor children to the innocent spouse subject to Article 213, and disqualifies the guilty spouse from inheriting from the innocent spouse by intestate succession. Grounds under Article 55 include repeated physical violence or grossly abusive conduct, sexual infidelity or perversion, drug addiction or habitual alcoholism, a subsequent bigamous marriage, an attempt on the petitioner's life, and abandonment without justifiable cause for more than one year. The petition must be filed within five years of the occurrence.

The landmark Supreme Court ruling in Tan-Andal v. Andal (2021) substantially reformed psychological incapacity under Article 36. The Court clarified that psychological incapacity is not a medical illness or personality disorder that requires a clinical psychiatrist's expert witness diagnosis; rather, it is a legal concept, and expert testimony is no longer indispensable. Ordinary witnesses who were present in the spouses' lives before the marriage, such as family members and friends, may testify on the behavior they consistently observed. The petitioner must still prove the incapacity by clear and convincing evidence.

Common misconceptions include believing that a long separation of 7 or 10 years, signing a private agreement before a notary public, or obtaining a mutual consent divorce abroad automatically ends a Philippine marriage. It does not. The Philippines does not recognize private separation or divorce agreements. A divorce obtained abroad is recognized only in limited cases—chiefly a marriage between a Filipino and a foreigner under Article 26 of the Family Code—and even then it must first be judicially recognized by a Philippine court before the Filipino spouse can rely on it and have it annotated in the civil registry.