Under Philippine law, marriage is a social institution recognized by the Family Code of the Philippines. The law sets forth clear requisites for a valid marriage. The absence, defect, or irregularity of these requisites impacts the validity of marriage in various ways, depending on the nature and extent of the issue. Here’s a comprehensive breakdown:

1. Requisites for a Valid Marriage (Article 2, Family Code)

Under Article 2 of the Family Code, a valid marriage requires both essential and formal requisites:

Essential Requisites:
1. Legal capacity of the contracting parties who must be a male and a female, at least 18 years old.
2. Consent freely given in the presence of the solemnizing officer.
Formal Requisites:
1. Authority of the solemnizing officer.
2. Valid marriage license (except in cases where the marriage is exempt from a license requirement).
3. Marriage ceremony with personal appearance before the solemnizing officer and at least two witnesses.

Failure to comply with these requisites may render the marriage either void or voidable, depending on the nature of the defect or irregularity.

2. Effects of Absence of Requisites

The Family Code establishes that the absence of certain requisites has a definitive effect on the validity of marriage:

Absence of Essential Requisites:
- Lack of Legal Capacity: If either party lacks legal capacity, such as being under 18 or of the same sex, the marriage is void ab initio (void from the start).
- Absence of Consent: If consent is absent or involuntary, it affects the validity. A marriage entered under duress, fraud, or without free will may be deemed voidable and annulled.
Absence of Formal Requisites:
- Absence of Authority of the Solemnizing Officer: If the person officiating the marriage lacks authority, the marriage is generally considered void unless one of the parties believed in good faith that the solemnizing officer had the authority.
- Absence of a Marriage License: A marriage without a license is void, except for those exempted by law, such as marriages in articulo mortis (when one or both parties are at the point of death), marriages among Muslims or members of ethnic communities, and marriages where parties have cohabited for at least five years and are free to marry each other.
- Absence of a Marriage Ceremony: Without a marriage ceremony, including personal appearance and the presence of witnesses, the marriage is void as the ceremony itself is essential to confirm the parties' intent to marry.

3. Defects or Irregularities in Requisites

Certain defects or irregularities may render a marriage voidable rather than void. A voidable marriage remains valid until annulled. Grounds and effects of such defects include:

Defect in Legal Capacity:
- Marriages contracted by parties aged 18-20 without parental consent, though irregular, are not void but subject to administrative sanctions.
Defect in Consent:
- Lack of Free Consent: Marriages may be annulled if consent was obtained through fraud, force, intimidation, or undue influence.
- Psychological Incapacity: If either party is psychologically incapacitated to comply with marital obligations, the marriage can be annulled. Psychological incapacity, as defined in Philippine law, must be a severe, permanent, and medically or clinically identifiable condition that prevents one from fulfilling essential marital duties.

4. Legal Presumptions and Good Faith

Good Faith Presumption: In cases where a marriage is declared void due to lack of a license, the parties who cohabited in good faith are presumed to have entered the marriage lawfully. Children born out of such void marriages are legitimate if at least one parent acted in good faith.
Bad Faith in Void Marriages: If both parties were in bad faith (i.e., both knew of the absence of a requisite), any children are considered illegitimate.

5. Effects on Property Relations and Status of Children

In marriages void ab initio due to absence of essential requisites, property relations revert to the status prior to marriage, applying rules on co-ownership. Children born of void marriages may be considered legitimate if the marriage is void solely due to defects in formal requisites and at least one parent acted in good faith.

In annulable marriages, the marriage remains valid until annulled. Property relations adhere to the matrimonial property regime until annulment. Children born before annulment are legitimate, and parental authority remains unaffected.

6. Judicial Declaration of Nullity and Annulment

Philippine law requires a judicial declaration of nullity for void marriages, meaning that parties must file a court case to have the marriage declared void. Annulable marriages require an annulment decree to dissolve the marriage, typically granted on grounds such as lack of consent, fraud, or psychological incapacity. Both processes have distinct legal effects:

Nullity of Void Marriages:
- No legal rights and obligations arise between the parties, except for limited cases concerning property and legitimacy of children.
- Upon nullity, parties revert to their single status and may remarry, provided the court order becomes final.
Annulment of Voidable Marriages:
- Marriage remains valid until annulled, affecting property relations, custody, and child support.
- Grounds such as lack of parental consent, unsound mind, fraud, and physical incapacity are common, with each ground having specific requirements under the Family Code.

7. Prescription Periods for Actions to Annul

Under Article 47 of the Family Code:

Actions to annul a marriage based on lack of parental consent must be filed by the non-consenting parent or guardian within five years after attaining the age of 21.
For marriages based on fraud, force, intimidation, or undue influence, actions must be filed within five years from the time of discovery of the defect or from the cessation of the threat or intimidation.

Summary Table: Effects of Absence, Defect, or Irregularity of Requisites

Issue	Effect on Marriage	Status of Children
Lack of Legal Capacity	Void	Illegitimate
Absence of Consent	Voidable (subject to annulment)	Legitimate if annulled
No Authority of Officer	Void	Legitimate if one acted in good faith
Absence of Marriage License	Void (subject to exceptions)	Legitimate if one acted in good faith
No Marriage Ceremony	Void	Illegitimate
Psychological Incapacity	Voidable	Legitimate until annulled

In conclusion, the Family Code stipulates that compliance with both essential and formal requisites is crucial for a valid marriage in the Philippines. Absence, defect, or irregularity in these requisites has specific legal consequences, ranging from annulment to a declaration of nullity, with corresponding effects on property relations and legitimacy of offspring.