Below is a comprehensive overview of adultery as defined and penalized under Philippine law, focusing on the legal action that may be taken for adultery involving a married woman. The discussion draws on the Revised Penal Code of the Philippines, pertinent rules of court procedure, and relevant jurisprudence. Please note that this information is for general educational purposes and does not substitute for personalized legal advice.

1. Definition and Governing Law

1.1. Adultery Under the Revised Penal Code

Legal Basis: Adultery in the Philippines is criminalized under Article 333 of the Revised Penal Code (RPC).
Definition: Adultery is committed by:
1. A married woman who engages in sexual intercourse with a man not her husband; and
2. The man who has carnal knowledge of the married woman, knowing her to be married (although jurisprudence has held that knowledge of the woman’s marital status may be implied from surrounding circumstances).

Essentially, adultery punishes the unfaithfulness of a wife and the man who cohabits or has sexual relations with her. By contrast, the crime committed by a husband who has extramarital relations is typically concubinage (Article 334, RPC), which has different elements and penalties.

1.2. Rationale of the Law

Historically, Philippine adultery law was based on the traditional principle of protecting the sanctity of marriage and punishing sexual infidelity on the part of a married woman (and the man who sleeps with her). Although some have called for modern updates to address gender biases, these provisions remain part of current law.

2. Elements of the Crime of Adultery

For a successful criminal complaint for adultery, the following elements must be proven:

Marriage: The woman is validly married to another person.
Sexual Intercourse: There is voluntary sexual intercourse between the married woman and a man who is not her husband.
Knowledge or Reasonable Belief of the Marriage: The man, in most cases, knows or has reason to know that the woman is married (though lack of knowledge is rarely a successful defense if circumstances reasonably point to awareness).

No habituality or multiple acts are necessary under Article 333. Each act of sexual intercourse can be charged as a separate count of adultery if discovered.

3. Filing a Criminal Case: Who, When, and How

3.1. Who May File

Adultery is considered a private crime under Philippine law. This means that only the offended spouse (the husband of the offending wife) can initiate or file the criminal complaint.
The State or other parties cannot commence the action on their own.

3.2. Indispensable Parties

Under Article 344 of the Revised Penal Code, if the husband files a complaint for adultery, he must include both his wife and her paramour as respondents. Failing to include one of them (unless there is a justifiable exception) can result in the complaint being dismissed.

3.3. Consent or Pardon

If the husband consented to or pardoned the adulterous act, he can no longer file an adultery complaint.
Consent implies prior knowledge and approval; pardon can be express or implied and typically happens after discovering the offense (e.g., cohabiting again with the wife under circumstances indicating forgiveness).

3.4. Where to File

The complaint-affidavit is usually filed before the Office of the City or Provincial Prosecutor where the adulterous act happened or where the complainant/witnesses reside.
A preliminary investigation will then determine if there is sufficient evidence to file the case in court.

3.5. Prescription Period

Adultery prescribes in five (5) years from the date the adulterous act was committed.
Since each act is treated as a separate offense, the period begins to run from the day of the commission of each act.
If the husband only recently discovered an act of adultery committed long ago, timing and proof of recent discovery can become a complex issue, but generally, the five-year period is counted from actual commission (subject to nuanced jurisprudence).

4. Evidence and Proving Adultery

4.1. Standard of Proof

As in all criminal cases, guilt must be proven beyond reasonable doubt.
Direct proof of the sexual act is not always possible; hence, circumstantial evidence is often used, such as:
- Caught in flagrante delicto (in the act).
- Testimony of witnesses who saw them enter a room under suspicious circumstances and remain there for a certain time.
- Love letters, messages, or other communications that strongly suggest a sexual affair.
- Pregnancy of the woman (if the husband can prove it is not his child and that the paramour is the father).

4.2. Challenges in Prosecution

Because adultery is a private crime and a delicate matter, prosecutors and courts tend to be strict in requiring convincing evidence.
Circumstantial proof can be enough if it leads to a moral certainty of guilt, but purely speculative suspicion is insufficient.

5. Penalties for Adultery

5.1. Imprisonment

Under Article 333 of the Revised Penal Code, the penalty for adultery is prisión correccional in its medium and maximum periods (i.e., from 2 years, 4 months, and 1 day to 6 years).
The duration of the penalty will be calibrated by the courts based on the severity or frequency of the acts, along with other mitigating or aggravating circumstances (if any).

5.2. Civil Liabilities

A criminal conviction for adultery may give rise to civil liability for damages. The husband may claim damages in the same proceeding, or file a separate civil action to recover damages for the shame or mental anguish suffered.

6. Legal Consequences and Other Remedies

6.1. Legal Separation

Adultery is a recognized ground for legal separation under Philippine law.
If a spouse obtains a decree of legal separation, it does not sever the marital bond (unlike annulment or declaration of nullity) but authorizes the spouses to live separately and terminates the regime of conjugal or community property.

6.2. Nullity or Annulment of Marriage

Adultery in itself is not a direct ground for annulment or declaration of nullity of marriage under Philippine law. Grounds for these actions are generally specified in the Family Code (e.g., lack of authority of solemnizing officer, lack of marriage license, psychological incapacity, etc.).
However, persistent infidelity could form part of the factual basis for a petition claiming psychological incapacity (if it is shown to be a manifestation of a personality disorder that renders a spouse incapable of fulfilling marital obligations).

6.3. Other Applicable Laws

If the adulterous relationship involves violence, coercion, or other forms of abuse (e.g., threats, blackmail), there might be ancillary civil or criminal liabilities under statutes such as the Anti-Violence Against Women and Their Children Act (R.A. 9262). However, that law typically protects women and their children; it is not ordinarily used to charge a wife’s extramarital partner unless specific violent acts or psychological abuse are involved.

7. Defenses and Limitations

7.1. Defense of Lack of Knowledge

The man may argue he did not know the woman was married. However, courts generally examine the totality of circumstances to see if such ignorance is credible.

7.2. Consent or Pardon

If the husband had previously consented to or forgiven the relationship, the complaint can be dismissed. Courts look for clear evidence of consent or pardon, e.g., the husband taking no action despite clear knowledge for a prolonged period, or reconciling in a manner that implies forgiveness.

7.3. Failure to Include One Party

If the complaint is directed only at the man or only at the married woman, the complaint may be dismissed, since the law requires both parties to be charged except under specific justified circumstances.

7.4. Expiry of Prescription Period

As noted, the charge may be time-barred if brought after more than five (5) years from the date of the adulterous act.

8. Practical Considerations and Advice

Gather Evidence Early: Since the burden is high (beyond reasonable doubt), the offended spouse is advised to gather strong, credible evidence before filing a complaint.
Consider Implications: A criminal case can be lengthy, expensive, and emotionally taxing. Some spouses opt for legal separation or civil suits for damages rather than pursuing a criminal charge.
Seek Legal Counsel: Before deciding to file a complaint, the husband is strongly encouraged to consult a lawyer to discuss the strength of evidence, the likelihood of success, and potential counterclaims or defenses.
Effect on Children: Criminal proceedings may affect not only the marital relationship but also children of the marriage. Factors such as custody and property arrangements should be weighed.

9. Conclusion and Disclaimer

Adultery involving a married woman remains a punishable crime under Philippine law, with clear legal prerequisites and procedures for prosecution. The offended spouse (husband) holds the exclusive right to initiate the complaint, and must include both the wife and her alleged paramour. The burden of proof is high, requiring careful gathering of evidence and strict adherence to procedural rules.

Disclaimer: This overview is for general informational purposes only and is not legal advice. Laws and legal procedures may change, and the outcome of any legal action will depend on specific facts and applicable jurisprudence. For personalized guidance, consult a qualified attorney experienced in family and criminal law in the Philippines.