In the moral theology of St. Thomas Aquinas, the moral act is determined by three factors or “fonts”, two of which reside within the acting person while the third is partially dependent upon the exterior world. Those fonts arising from inside the person are delineated as the object or means of the act, its efficient cause and the matter of which it consists, and the intention of the act, its end or final cause, the form to which the person tends in acting. In essence, these two factors determine the morality of an act. The third factor, partially derived from the environmental situation of the agent, is the circumstance of the act; this includes its unintended consequences, other moral agents who are influencing or affected by the act, and the prerequisites for the moral act itself, such as the voluntariness or consent of the act, the matter required for the act, etc., all of which can influence the quality or severity of the act. These three fonts provide a framework for judging the imputability of moral acts and establish their integral sequence in human nature.

The first font, the object, is the efficient cause of the moral act, the means chosen by the intellect and employed by the will in order to accomplish its end. Although it is not the first cause of the moral act, which would be the final cause of its end-goal, the object is an equal factor in determining the moral value of an act, constituting the concrete steps by which someone accomplishes their intention. Object is sometimes used in a way that describes the intention or end of an action, analogous to the “direct object” of an action in a sentence, but in St. Thomas’s moral theory, the object specifies the means chosen to attain an end; it is thus distinct in notion but inseparable in act from the intention. For example, the (primary) intention of Catholic apologetics is the conversion of souls to Christ (a secondary intention may be the defense of Catholic teaching against disputations). While this intention is good, if the means used to achieve it are wrong, such as ad hominem attacks violating the dignity of the person or coercive, sophistical arguments justifying Catholic teaching or misrepresenting the ideas of others, the act becomes evil by presuming that the ends can justify the means, and more often than not the intention will also be forfeited when the other person realizes the evil means for what they are and therefore rejects the apologist and what he stands for.

The second font, the intention, is the final cause of the moral act, the end or goal desired by the will as a good judged by the intellect. As the final cause, the intention is the first cause and motivator of the moral act, without which the means would not be chosen and the circumstances would be irrelevant. It is what first moves the agent to act and what, in its accomplishment, completes the act. It is the reason for acting in the first place. The intention is not precisely the same as the effects of an act since its effects can be unintended and therefore carry little to no moral weight. Therefore, the consequences of an act fall more into the font of circumstance rather than intention. The choice of the end precedes and initiates the action and is based more in prudence; it requires judging one’s intention according to objective moral standards, including natural, human and divine law. To pursue an evil end, even without ever accomplishing it, entails some degree of evil in the agent, a corruption of prudential judgment and the desire of the will. Alternatively, a good intention cannot ever justify evil means, nor can positive consequences justify an evil intention. It could be said that the root of the expression “the road to Hell is paved with good intentions” refers to this fact, since a good intention is corrupted by the use of evil means while an evil intention is not abrogated by good consequences. Following the previous example, if a Catholic apologist’s intention is merely to defeat an opponent, to gloat over his victory for self-aggrandizement, his apologetics are evil, even if the means of argument used are good and even if an unintended consequence of his arguments is the eventual conversion of the other person.

The third font, the circumstances, includes both interior and exterior conditions which are either prerequisites for the act or which can influence its moral degree. This can include the three traditional conditions for an act to be considered a mortal sin, namely the agent’s consent, his knowledge of the evil nature of the act and the severity of the act itself, none of which can make an act good or evil but simply affect the culpability of the agent and take factors into consideration such as the ignorance, immaturity, mental instability, etc. of the agent. Exteriorly, the circumstances can include the requisite materials needed to accomplish an action at all, since an impossible action, even if intended, cannot be performed, and the attempt to use improper or invalid materials to accomplish an act can cause it to be more or less evil; it also includes influences from other people or the environment, which may limit the means, hinder the intention or otherwise subvert the person from accomplishing an act, as well as the consequences of an act. Continuing the previous examples, if a Catholic apologist is unaware, through no fault of his own, that a particular position is not in fact good but he argues that it is, his act would still be wrong but his culpability for it would be reduced. Similarly, if an apologist advises someone that it is good to give money to the homeless, but a homeless person to whom she donates uses the money to commit a crime, the apologist is not culpable for the consequences of his advice, nor is the donor for her charity.

The three font theory of Thomistic moral theology helps to explain and clarify the nature of human action. These factors can often be neglected or simply unknown to many people, including Catholics, leading them to believe they are guilty when they are not, such as for the unintended (non-negligent) consequences of their good acts, or to commit grave evils which they justify by good intentions. For this reason, it is essential to have a good grasp of St. Thomas’s theory, for Catholics and non-Catholics alike, and is also necessary to properly participate in the Sacrament of Confession, so that our real guilt can be ascertained by an examination of conscience and in the judgment of the priest.