A crime is an act or omission made punishable
Felony is defined under the code as an act or omission punishable by law, committed through culpa or dolo.  The words “punishable by law" means that the act or omission must be defined and punished by the Revised Penal Code and no other law. Dolo is a Spanish term which means deceit. There is deceit when an act is performed with deliberate intent.  Culpa is also a Spanish term which means fault. There is fault when a wrongful act results from negligence, imprudence, lack of skill or foresight. Here lies the confusion. The Code specifically provides for a definition of a felony, but nevertheless simultaneously uses the word crime or offense in describing the acts and omissions punishable by the code. A crime is defined as an act or omission which is made punishable by law. On the other hand, an offense includes both felony and crime, as it is generally referred to as violations of the law.
A person incurs criminal liability either by committing a felony regardless of the original intent of the actor or by committing an impossible crime.  The law punishes both intentional and unintentional felonies. The rationale behind the liability incurred for an intended act is simple: a person must be held liable for an act or omission which the law specifically prohibits. On the other hand an unintentional act is punishable because of the lack of skill (negligence) or lack foresight (imprudence) which makes it as if it was intentional. The provision seems to define only the liability of a principal and excludes that of the accessory and accomplice.
Members of the Judiciary are required, under the code, to make a report to the president whenever there is an act that should be repressed but is not made punishable by any law.  This provision of the Code has never been used. This is because the duty to make laws, under the Constitution, is with the Congress, and not the President.  Also, the Congress may conduct an investigation in aid of legislation. 
Circumstances affecting Criminal Liability
There are circumstances which are attendant in the commission of an offense which have the effect of increasing the penalty or lowering the penalty imposed. Also, there are acts which are considered to be wholly excusable if a certain circumstance is attendant in the commission of the felony. The Code provides for justifying, exempting, mitigating, aggravating and alternative circumstances which alter the penalty imposed if it is attendant in the commission of the offense. Absolutory causes, which exempt an offender from criminal liability, may also be found in the Code, although not found in one provision.
a. Justifying and Exempting Circumstances
Justifying Circumstances are those where the act of a person is said to be in accordance with law so that such person is deemed not to have transgressed the law and is free from criminal and civil liability.  The following circumstances, if present in the commission of a felony, serve to free the offender of any liability:
“Article 11. Justifying circumstances. - The following do not incur any criminal liability:
1. Anyone who acts in defense of his person or rights, provided that the following circumstances concur;
First. Unlawful aggression;
Second. Reasonable necessity of the means employed to prevent or repel it;
Third. Lack of sufficient provocation on the part of the person defending himself.
2. Any one who acts in defense of the person or rights of his spouse, ascendants, descendants, or legitimate, natural or adopted brothers or sisters, or of his relatives by affinity in the same degrees, and those by consanguinity within the fourth civil degree, provided that the first and second requisites prescribed in the next preceding circumstance are present, and the further requisite, in case the provocation was given by the person attacked, that the one making defense had no part therein.
3. Anyone who acts in defense of the person or rights of a stranger, provided that the first and second requisites mentioned in the first circumstance of this article are present and that the person defending be not induced by revenge, resentment, or other evil motive.
4. Any person who, in order to avoid an evil or injury, does an act which causes damage to another, provided that the following requisites are present;
First. That the evil sought to be avoided actual exists;
Second. That the injury feared be greater than that done to avoid it;
Third. That there be no other practical and less harmful means of preventing it.
5. Any person who acts in the fulfillment of a duty or in the lawful exercise of a right or office.
6. Any person who acts in obedience to an order issued by a superior for some lawful purpose." 
No crime is committed therefore no civil liability attaches. The burdens of proving the existence of a justifying circumstance lie with the accused.  When an accused invokes self defense, it is incumbent upon him to prove such by clear and convincing evidence. 
On the other hand, Exempting Circumstances are those grounds exemption from punishment because there is wanting in the agent of the crime any of the conditions which make the act voluntary or negligent.  The following are exempting circumstances:
“Article 12. Circumstances which exempt from criminal liability. - The following are exempt from criminal liability:
1. An imbecile or an insane person, unless the latter has acted during a lucid interval.
When the imbecile or an insane person has committed an act which the law defines as a felony (delito), the court shall order his confinement in one of the hospitals or asylums established for persons thus afflicted, which he shall not be permitted to leave without first obtaining the permission of the same court.
2. A person under nine years of age.
3. A person over nine years of age and under fifteen, unless he has acted with discernment, in which case, such minor shall be proceeded against in accordance with the provisions of article 80 of this Code.
When such minor is adjudged to be criminally irresponsible, the court, in conformity with the provisions of this and the preceding paragraph, shall commit him to the care and custody of his family who shall be charged with his surveillance and education; otherwise, he shall be committed to the care of some institution or person mentioned in said article 80.
4. Any person who, while performing a lawful act with due care, causes an injury by mere accident without fault or intention of causing it.
5. Any person who acts under the compulsion of irresistible force.
6. Any person who acts under the impulse of an uncontrollable fear of an equal or greater injury.
7. Any person who fails to perform an act required by law, when prevented by some lawful insuperable cause." 
According to Guevara  one who acts because of an exempting circumstance commits a crime, but because of the absence of voluntariness there is no criminal liability, only civil liability. The burden of proving, with clear and convincing evidence, that the accused acted with the existence of an exempting circumstance lies with the accused.
b. Mitigating Circumstances
Mitigating Circumstances are those which, if present in the commission of the crime, do not entirely free the actor from criminal liability, but serve only to reduce the penalty.  Diminution of the freedom or intelligence is the basis for the mitigation.  The Code provides the following circumstance which mitigate criminal liability:
“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." 
Mitigating Circumstances are classified into two groups: Ordinary and Privileged. Ordinary Mitigating circumstances are those enumerated in Article 13, save minority, which is the effect of the lowering of the age responsibility. An ordinary mitigating circumstance has the effect of reducing the penalty a period lower. Privileged mitigating circumstance are those which are enumerated by law as such, and has the effect of reducing the penalty a degree or two lower. The existence of two ordinary circumstances has the effect of a privileged, lowering the penalty by a degree or two. A privileged mitigating circumstance cannot be offset by an aggravating circumstance, whereas the ordinary one may.
c. Aggravating Circumstances
Aggravating Circumstances are those which, if present in the commission of a crime, serve to increase the penalty without, however, exceeding the maximum penalty, allowed by law for the offense.  The Code enumerates twenty-one circumstances which aggravate criminal liability, they are the following:
“Article 14. Aggravating circumstances. - The following are aggravating circumstances:
1. That advantage be taken by the offender of his public position.
2. That the crime be committed in contempt of or with insult to the public authorities.
3. That the act be committed with insult or in disregard of the respect due to the offended party on account of his rank, age, or sex, or that it be committed in the dwelling of the offended party, if the latter has not given provocation.
4. That the act be committed with abuse of confidence or obvious ungratefulness.
5. That the crime be committed in the palace of the Chief Executive, or in his presence, or where public authorities are engaged in the discharge of their duties, or in a place dedicated to religious worship.
6. That the crime be committed in the nighttime, or in an uninhabited place, or by a band, whenever such circumstances may facilitate the commission of the offense.
Whenever more than three armed malefactors shall have acted together in the commission of an offense, it shall be deemed to have been committed by a band.
7. That the crime be committed on the occasion of a conflagration, shipwreck, earthquake, epidemic, or other calamity or misfortune.
8. That the crime be committed with the aid of armed men or persons who insure or afford impunity.
9. That the accused is a recidivist.
A recidivist is one who, at the time of his trial for one crime, shall have been previously convicted by final judgment of another crime embraced in the same title of this Code.
10. That the offender has been previously punished for an offense to which the law attaches an equal or greater penalty or for two or more crimes to which it attaches a lighter penalty.
11. That the crime be committed in consideration of a price, reward, or promise.
12. That the crime be committed by means of inundation, fire, poison, explosion, stranding of a vessel or intentional damage thereto, derailment of a locomotive, or by the use of any other artifice involving great waste and ruin.
13. That the act be committed with evident premeditation.
14. That craft, fraud, or disguise be employed.
15. That advantage be taken of superior strength, or means be employed to weaken the defense.
16. That the act be committed with treachery (alevosia).
There is treachery when the offender commits any of the crimes against the person, employing means, methods, or forms in the execution thereof which tend directly and specially to insure its execution, without risk to himself arising from the defense which the offended party might make.
17. That means be employed or circumstances brought about which add ignominy to the natural effects of the act.
18. That the crime be committed after an unlawful entry.
There is an unlawful entry when an entrance is effected by a way not intended for the purpose.
19. That as a means to the commission of a crime a wall, roof, floor, door, or window be broken.
20. That the crime be committed with the aid of persons under fifteen years of age or by means of motor vehicles, motorized watercraft, airships, or other similar means. (As amended by Rep. Act No. 5438, approved Sept. 9, 1968.)
21. That the wrong done in the commission of the crime be deliberately augmented by causing other wrong not necessary for its commission." 
There are four kinds of aggravating circumstance, namely: generic, specific, qualifying and inherent. Generic circumstances are those which generally apply to all crimes such as dwelling and recidivism. Those which apply only to particular crimes are Specific circumstances. Those that change the nature of the offense are called Qualifying circumstance. And that which necessarily accompanies the commission of the crime is called Inherent circumstance. Qualifying circumstances must be alleged and prove to have the necessary effect. The appreciation of a qualifying circumstance, even if it is not alleged, constitutes a violation of the constitutional right to be informed of the nature and cause of the accusation against him. A qualifying circumstance changes the nature of the offense committed, therefore, an integral part of the offense. If such is not alleged, it may be proved during the course of the trial, but will only be considered as a generic circumstance. 
d. Alternative Circumstances
Alternative Circumstances are those which must be taken into consideration as aggravating or mitigating according to the nature and effects of the crime and other conditions attending its commission.  There are three alternative circumstances: Relationship, Intoxication and Degree of Instruction or education of the offender. The provision of law which enumerates the alternative circumstance does not say when exactly, save for intoxication, such shall be considered as aggravating or mitigating.