Every action and the only one that proceeds from the deliberate will of a human being. Consequently it proceeds from the knowledge of the intellect and the free decision of the human will. It is an act of which a human being is the master, whether the act begins and ends in the will, i.e., elicited act (such as love), or the will affects another faculty, i.e., commanded act (such as writing). Only human acts are morally imputable to the one who performs them, unlike what are called acts of a human being performed by persons who lack the use of reason or whose freedom is totally inhibited as in sleep or under anesthesia.
Human acts are either good or bad, depending on whether they agree or disagree with the norms of morality. Morally indifferent human acts are purely theoretical. In practice all deliberate actions are somehow either morally good or bad.
Similarly the distinction between natural and supernatural actions is more speculative than real, since whatever a person does deliberately has moral significance for his or her supernatural destiny.
For juridical reasons, which may partake of divine law, human acts may be either valid or invalid, according as they fulfill the conditions required by Church law. Thus baptism administered with some liquid other than water is not valid.