Answer
Aggravating circumstances, enumerated in Article 14 of the Revised Penal Code, are those that increase the offender's criminal liability because they reveal greater perversity — for example, taking advantage of public position, committing the crime with treachery or evident premeditation, abuse of superior strength, commission in the offended party's dwelling, with the aid of armed men, or by means of fire, poison, or explosion.
Their effect is governed by Articles 62 to 64: a generic aggravating circumstance, when not offset by a mitigating one, raises the penalty to its maximum period. Circumstances that are inherent in the crime, or that are themselves elements of the offense, are not counted again; and a qualifying aggravating circumstance (such as treachery in murder) changes the very nature of the crime rather than merely adjusting the period. Aggravating circumstances must generally be alleged in the information to be appreciated.