An indispensable requisite of self-defense is that the victim must have mounted an unlawful aggression against the accused. Without such unlawful aggression, the accused cannot invoke self-defense as a justifying circumstance.

An indispensable requisite of self-defense is that the victim must have mounted an unlawful aggression against the accused. Without such unlawful aggression, the accused cannot invoke self-defense as a justifying circumstance.
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 In order for self-defense to be appreciated, he had to prove by clear and convincing evidence the following elements: (a) unlawful aggression on the part of the victim; (b) reasonable necessity of the means employed to prevent or repel it; and (c) lack of sufficient provocation on the part of the person defending himself.¹⁹ Unlawful aggression is the indispensable element of self-defense, for if no unlawful aggression attributed to the victim is established, self-defense is unavailing, for there is nothing to repel.²⁰ The character of the element of unlawful aggression is aptly explained as follows:

Unlawful aggression on the part of the victim is the primordial element of the justifying circumstance of self-defense. Without unlawful aggression, there can be no justified killing in defense of oneself. The test for the presence of unlawful aggression under the circumstances is whether the aggression from the victim put in real peril the life or personal safety of the person defending himself; the peril must not be an imagined or imaginary threat. Accordingly, the accused must establish the concurrence of three elements of unlawful aggression, namely: (a) there must be a physical or material attack or assault; (b) the attack or assault must be actual, or, at least, imminent; and (c) the attack or assault must be unlawful.

Unlawful aggression is of two kinds: (a) actual or material unlawful aggression; and (b) imminent unlawful aggression. Actual or material unlawful aggression means an attack with physical force or with a weapon, an offensive act that positively determines the intent of the aggressor to cause the injury. Imminent unlawful aggression means an attack that is impending or at the point of happening; it must not consist in a mere threatening attitude, nor must it be merely imaginary, but must be offensive and positively strong (like aiming a revolver at another with intent to shoot or opening a knife and making a motion as if to attack). Imminent unlawful aggression must not be a mere threatening attitude of the victim, such as pressing his right hand to his hip where a revolver was holstered, accompanied by an angry countenance, or like aiming to throw a pot.²¹