The circumstances which mitigate criminal liability are enumerated in Article 13 of the Revised Penal Code. It reads:
Article 13. Mitigating circumstances. - The following are mitigating circumstances:
1. Those mentioned in the preceding chapter, when all the requisites necessary to justify the act or to exempt from criminal liability in the respective cases are not attendant.
2. That the offender is under eighteen years of age or over seventy years. In the case of the minor, he shall be proceeded against in accordance with the provisions of article 80.
3. That the offender had no intention to commit so grave a wrong as that committed.
4. That sufficient provocation or threat on the part of the offended party immediately preceded the act.
5. That the act was committed in the immediate vindication of a grave offense to the one committing the felony (delito) his spouse, ascendants, descendants, legitimate, natural or adopted brothers or sisters or relatives by affinity within the same degrees.
6. That of having acted upon an impulse so powerful as naturally to have produced passion or obfuscation.
7. That the offender had voluntarily surrendered himself to a person in authority or his agents, or that he had voluntarily confessed his guilt before the court prior to the presentation of the evidence for the prosecution.
8. That the offender is deaf and dumb, blind or otherwise suffering some physical defect which thus restricts his means of action, defense, or communication with his fellow beings.
9. Such illness of the offender as would diminish the exercise of the will-power of the offender without however depriving him of consciousness of his acts.
10. And, finally, any other circumstance of a similar nature and analogous to those above mentioned.
Effect of mitigating circumstances
Both aggravating circumstance and mitigating circumstance are established in the Revised Penal Code for the purpose of increasing or decreasing the penalty to be imposed, according to the greater or lesser seriousness of the crime committed, either by itself or arising from the defendant's moral attributes.<ref>People vs. Tanyaquin, G.R. No. L-37124, 28 October 1932</ref> The following rules<ref>Article 62, Revised Penal Code</ref> shall be observed in considering aggravating circumstances:
- When in the commission of the crime, advantage was taken by the offender of his public position, the penalty to be imposed shall be in its maximum regardless of mitigating circumstances.
- The maximum penalty shall be imposed if the offense was committed by any person who belongs to an organized/syndicated crime group. An organized/syndicated crime group means a group of two or more persons collaborating, confederating or mutually helping one another for purposes of gain in the commission of any crime.
- Mitigating circumstances which arise from the moral attributes of the offender, or from his private relations with the offended party, or from any other personal cause, shall only serve to aggravate or mitigate the liability of the principals, accomplices and accessories as to whom such circumstances are attendant.
- The circumstances which consist in the material execution of the act, or in the means employed to accomplish it, shall serve to aggravate or mitigate the liability of those persons only who had knowledge of them at the time of the execution of the act or their cooperation therein.
The mitigating circumstances
Passion and obsfuscation
For the mitigating circumstance of passion and obfuscation to exist, it is necessary that the act which gave rise to the obfuscation be not removed from the commission of the offense by a considerable length of time, during which period the perpetrator might recover his normal equanimity.<ref>People vs. Layson, G.R. No. L-25177, 31 October 1969</ref>
Some circumstances [i.e., the relationship between the offender and the victim, intoxication of the offender, the degree of instruction and education of the offender) may be taken into consideration as aggravating or mitigating according to the nature and effects of the crime and the other conditions attending its commission. These are called alternative circumstances.