There are three fonts of morality: 1. intention, 2. moral object, 3, circumstances. Each and every knowingly chosen act of the human person has three fonts, and all three fonts must be good for the act to be moral (morally licit; permissible without sin). If any one font is bad, the act is immoral; it is a sin. Under the eternal moral law, an act (or ‘human act’) is a knowing choice; it is an exercise of will and intellect.
Sexual ethics is no exception to the basic principles of ethics. There are still three fonts of morality for sexual acts: 1. intention, 2. moral object, 3, circumstances. Each and every knowingly chosen sexual act of the human person has three fonts, and all three fonts must be good for the sexual act to be moral (morally licit; permissible without sin). If any one font is bad, the sexual act is immoral; it is a sin. Under the eternal moral law, a sexual act is a knowing choice; it is the deliberate choice to use the genital sexual faculty.
When any act is done with bad intention, the act is a sin. But if the only font causing your act to be immoral is your intention, then, by the use of free will in cooperation with grace, you can change your intention. Choose a good intention.
When any act is done with bad circumstances, that is, when the reasonably anticipated bad consequences outweigh the reasonably anticipated good consequences, then the choice of that act is a sin. It is a sin to choose to do more harm than good. However, circumstances can change, or a person might change the circumstances by some other moral act or set of moral acts, so that the good would then outweigh the bad.
The moral object is the end, in terms of morality, toward with the knowingly chosen act of the human person is inherently ordered. When the human person chooses any act with an evil moral object, that is, when the human person intentionally (deliberately, voluntarily) chooses a type of act which is, by its very nature, ordered toward an evil moral object, then the act is intrinsically evil; it is always a sin by the very nature of the act. These intrinsically evil acts cannot be made moral by a change in intention, nor by a change in circumstances. The only moral option is to choose a different type of act, one that is inherently ordered toward only good, not evil. Intrinsically evil acts are always a sin.
Sacred Congregation for the Doctrine of the Faith: “Now according to Christian tradition and the Church’s teaching, and as right reason also recognizes, the moral order of sexuality involves such high values of human life that every direct violation of this order is objectively serious.” (CDF, Persona Humana, n. X.)
Some intrinsically evil acts are venial sins (such as a venial lie), and other intrinsically evil acts are mortal sins (such as murder). But every sexual sin that is intrinsically evil is objectively a mortal sin. For such sins are, by their very nature, a direct violation of the good required of sexual acts by the eternal moral law. Every intrinsically evil sexual act is always gravely immoral.
What is the moral object of moral sexual acts? To be moral, each and every sexual act must be marital and unitive and procreative. These three moral objects of the sexual act are required by the eternal moral law, by the love of God and neighbor. Every non-marital sexual act is intrinsically evil and always gravely immoral. Every extra-marital sexual act (e.g. premarital sex, or adultery) is intrinsically evil and always gravely immoral. Every non-procreative sexual act is intrinsically evil and always gravely immoral. Every contracepted sexual act is intrinsically evil and always gravely immoral. Every non-unitive sexual act (e.g. homosexual acts, or unnatural sexual acts between a man and woman) is intrinsically evil and always gravely immoral. Even between a husband and wife, all unnatural sexual acts are intrinsically evil and always gravely immoral.
The deprivation of any one of these three goods — the marital, unitive, and procreative meanings — makes the moral object evil and the act inherently immoral and a grave sin. If any act is deprived of two or three of these good moral objects, then the act is even more gravely disordered, due to a greater deprivation of the goods required by the moral law.
The only moral sexual act is natural marital relations open to life.
Ronald L. Conte Jr.
Roman Catholic theologian and Bible translator