It is by no means self-evident why there is an absolute break between light and grave matter and so between venial and mortal sin. Any immoral act is contrary to integral human fulfillment and so, as we have seen, to divine goodness; yet a venial sin is not incompatible with love of God, and some sins are venial because of light matter. The explanation that God simply decrees that some sins will not be mortal cannot be accepted. But how can the real evil of venial sin coexist in one’s heart with love of God?
In recent years some Catholic theologians have proposed versions of fundamental-option theory. The basic idea is that a person is disposed toward or against God, not by any ordinary free choice, but by a comprehensive orientation of the whole self. Some treat fundamental option as a basic commitment, others as something more mysterious—a total self-disposal attributed not to free choice, but to a freedom outside experience, often called “fundamental freedom” or “basic freedom.”
Fundamental-option theory distinguishes between those acts which establish or alter fundamental option and those which do not. The matter of acts of the first sort is grave, while the matter of acts of the second sort is light. (Thus there are grave and light good acts as well as bad ones.) Many current theories suggest that even a fully deliberate immoral choice of grave matter need not break one’s friendship with God.
Rather than explaining why some matters are likely to subvert a good fundamental option and others are not, however, current theories aggravate the problem. The fundamental option of a Christian is supposed to be love of God (in the case of a nonbeliever, a commitment to moral uprightness); but the problem about grave and light matter arises precisely because any deliberate sin seems at odds with these standards.
Besides failing to resolve this problem, current fundamental-option theories have factual and logical difficulties. It is not demonstrated that everybody makes a fundamental option or that there is a fundmental freedom apart from free choice. The love of God poured forth in the hearts of believers, which transforms fallen human beings, is a divine gift, not an act of human self-disposal. Many proponents of fundamental option have an impoverished view of free choice which fails to do justice to its self-determining character. And the assertion that repeated oscillation between mortal sin and repentance is impossible is simply question-begging. As a practical matter, the main point of current fundamental-option theories has been to allow that some acts traditionally considered mortal sins need not be; such theories cannot be reconciled with the teaching of the Council of Trent on penance and mortal sin.
St. Thomas Aquinas explains grave matter and light matter on the basis that some kinds of acts are incompatible with charity between humankind and God or within humankind, while some are not. His treatment does not solve the problem. Still, it is helpful in calling attention to the fact that mortal sins disrupt existential harmony on its various levels as venial sins do not.
The solution to the problem seems to lie in a synthesis of his account and certain insights of fundamental-option theory. The fundamental option of Christian life is the act of faith. This is not simply an option for God or moral goodness; it has specific determinations, a definite content. This commitment excludes not only sins against faith but, implicitly, acts of any kind inconsistent with living as a member of the Church: These involve grave matter. Anything which the Church herself clearly and firmly teaches to be grave matter certainly is at odds with the act of living faith. Light matter, by contrast, is the matter of morally evil acts which violate neither the specific requirements of the act of faith nor any of its implications for ecclesial life.
Finally, there is an objection that some matters traditionally considered grave seem “purely personal” and have nothing to do with one’s relationship with God or the Church. The answer is that Christian life, as St. Paul points out, is not individualistic but is life in and for Jesus, and this has implications even for “purely personal” actions.