In the Philippine legal system, where absolute divorce is currently not recognized for non-Muslim Filipinos, an Annulment or a Declaration of Nullity of Marriage serves as the primary legal recourse for dissolving or voiding a marital union. While often used interchangeably in casual conversation, these are distinct legal concepts governed by the Family Code of the Philippines.

1. Void vs. Voidable Marriages

To understand the grounds, one must first distinguish between a marriage that is void from the beginning (void ab initio) and one that is voidable.

Void Marriages (Declaration of Nullity): These marriages are considered to have never existed in the eyes of the law. They cannot be "ratified" or cured by the parties staying together.
Voidable Marriages (Annulment): These marriages are considered valid until they are set aside by a court decree. They can often be "ratified" if the parties continue to live together after the cause for annulment has ceased.

2. Grounds for Declaration of Nullity (Void Marriages)

Under Articles 35, 36, 37, and 38 of the Family Code, a marriage is void from the beginning if:

Lack of Essential Requisites: Either party was under 18 years of age; the marriage was solemnized by an unauthorized person; or there was no valid marriage license.
Bigamous or Polygamous Marriages: A person marries while still being legally married to someone else.
Mistake in Identity: One party married the other under the belief they were someone else.
Psychological Incapacity (Article 36): This is the most common ground cited in Philippine courts. It refers to a party’s inability to comply with the essential marital obligations (mutual love, respect, support, and fidelity) due to a psychological condition that existed at the time of the marriage, even if it only manifested later.
Incestuous Marriages: Marriages between ascendants and descendants (e.g., parent and child) or between brothers and sisters, whether full or half-blood.
Public Policy Grounds: Marriages between collateral blood relatives up to the fourth civil degree (first cousins) or between step-parents and step-children.

3. Grounds for Annulment (Voidable Marriages)

Under Article 45, a marriage may be annulled for the following reasons, provided the petition is filed within the prescriptive period:

Lack of Parental Consent: If either party was between 18 and 21 years old and did not obtain consent from parents or guardians.
Insanity: Either party was of unsound mind at the time of the marriage, unless they freely cohabited after coming to reason.
Fraud: Consent was obtained through deceptive means. Legal fraud is strictly limited to:

Non-disclosure of a prior conviction involving moral turpitude.
Concealment by the wife of pregnancy by another man.
Concealment of a sexually transmitted disease (STD).
Concealment of drug addiction, habitual alcoholism, or homosexuality/lesbianism.

Force, Intimidation, or Undue Influence: Consent was obtained through threats or "shotgun" weddings.
Impotence: Physical inability to consume the marriage which appears to be incurable and was unknown to the other party.
Serious and Incurable STD: One party has a serious, incurable sexually transmitted disease existing at the time of the marriage.

4. Legal Requirements and Process

The process is rigorous and can take several years. The general steps and requirements include:

The Petition

A verified Petition for Annulment or Declaration of Nullity must be filed in the Regional Trial Court (Family Court) of the province or city where either the petitioner or the respondent has resided for at least six months prior to the filing.

Psychological Evaluation

In cases involving Article 36 (Psychological Incapacity), it is standard practice to undergo an evaluation by a clinical psychologist or psychiatrist. Their findings are presented as expert testimony to prove that the incapacity is grave, has "juridical antecedence" (existed before the wedding), and is incurable.

Collusion Investigation

The law strictly prohibits "quickie" or "consensual" annulments. After the petition is filed, the Public Prosecutor (Office of the Solicitor General) is tasked with investigating whether collusion exists between the parties—meaning they haven't fabricated the grounds just to get out of the marriage.

Mandatory Pre-Trial

The court will call for a pre-trial conference where the issues are simplified. The petitioner must personally appear; failure to do so can result in the dismissal of the case.

Trial and Evidence

The petitioner must present witnesses (including the expert witness, if applicable) and documentary evidence to prove the grounds cited. The State, represented by the Prosecutor, will cross-examine the witnesses to ensure the integrity of the proceedings.

Decree of Annulment

If the judge is satisfied with the evidence, a Decision is rendered. Once the decision becomes final and executory, a Decree of Annulment or Nullity is issued. This must be registered with the Local Civil Registrar and the Philippine Statistics Authority (PSA) to update the parties' marital status.

5. Effects on Children and Property

Status of Children: Children born of voidable marriages (annulment) or marriages declared void under Article 36 are considered legitimate. Children of other void marriages are generally considered illegitimate unless specified otherwise by law.
Property Relations: The absolute community of property or conjugal partnership is dissolved. The court will oversee the partition of assets and liabilities.
Right to Remarry: Once the Decree is registered and the "Certificate of Finality" is issued, both parties regain the legal capacity to remarry.