Unnatural sexual acts are intrinsically evil and always gravely immoral.
An unnatural sexual act is any deliberate use of the sexual faculty that is non-unitive and non-procreative. Such acts include oral, anal, or manipulative sex, with or without sexual climax. The presence or absence of sexual climax does not change the moral object of the act; the essential moral nature of the act itself remains the same. Even though some unnatural sexual acts have a type of mere physical union, it is not union as God intends in the use of human sexuality. Therefore, all such acts are deprived of the unitive meaning in the moral object; they are non-unitive sexual acts. Unnatural sexual acts are also non-procreative, since such acts are not the type of act inherently capable of procreation. Only natural intercourse (genital-to-genital intercourse between a man and a woman) is inherently capable of procreation, and therefore retains the procreative meaning in the moral object.
All unnatural sexual acts are intrinsically evil and always gravely immoral because they are deprived of the unitive and procreative meanings in their moral object. Such acts are never justified by being done within marriage, since the presence of the marital meaning cannot substitute for the lack of the unitive and procreative meanings in the moral object.
“Each and every sexual act in a marriage needs to be open to the possibility of conceiving a child.” (USCCB Catechism, p. 409) Unnatural sexual acts are not open to life, therefore unnatural sexual acts are not moral, even within marriage.
Neither can one or more procreative sexual acts be used to justify prior, concurrent, or subsequent unnatural sexual acts. For each and every sexual act in marriage must be procreative and unitive in order to be moral. It is not valid to argue, as a justification for sexual acts that are non-unitive and therefore non-procreative, that such acts would merge with unitive procreative acts of past and future to form a single moral unity, and so be qualified by exactly the same moral goodness as these. For every knowingly chosen act of the human person is subject to the same eternal moral law.
Calling an unnatural sexual act ‘foreplay’ does not justify that act. Licit foreplay must be good in itself. Licit foreplay is a good means to the good end of natural marital relations open to life. But it is never moral, even for the gravest reasons, to commit an intrinsically evil act so as to achieve a good end. The end never justifies the means. Therefore, intrinsically evil acts do not become moral by being used as a type of foreplay, as an intrinsically evil means to the good end of natural marital relations open to life.
Contraception is gravely immoral even in marriage for the same reason: the presence of the marital and unitive meanings cannot substitute for the lack of the procreative meaning, and any good end that might be intended in the use of contraception cannot justify the use of an intrinsically evil means, contraception, to that end.
When any act is deprived of any one or more of these three aspects of the good moral object of sexual relations (the unitive, procreative, and marital meanings), then the act is intrinsically evil. For such an act is inherently ordered toward a moral object that is deprived of one or more of these three good required by the love of God and the love of neighbor as self.
Every unnatural sexual act is intrinsically evil, even within marriage, because this type of sexual act does not have both the unitive and procreative meanings joined in the same act. In order to be moral, each and every sexual act must be marital, unitive, and procreative.
Pope Pius XI: “But no reason, however grave, may be put forward by which anything intrinsically against nature may become conformable to nature and morally good. Since, therefore, the conjugal act is destined primarily by nature for the begetting of children, those who, in exercising it, deliberately frustrate its natural power and purpose, sin against nature and commit a deed which is shameful and intrinsically vicious.
“Since, therefore, openly departing from the uninterrupted Christian tradition, some recently have judged it possible solemnly to declare another doctrine regarding this question, the Catholic Church, to whom God has entrusted the defense of the integrity and purity of morals, standing erect in the midst of the moral ruin which surrounds her, in order that she may preserve the chastity of the nuptial union from being defiled by this foul stain, raises her voice in token of her divine ambassadorship and through Our mouth proclaims anew: any use whatsoever of matrimony exercised in such a way that the act is deliberately frustrated in its natural power to generate life is an offense against the law of God and of nature, and those who indulge in such are branded with the guilt of a grave sin.” (Casti Connubii, n. 54-56.)
The purpose for which an act is chosen, and the deliberate choice of the act itself (whose moral nature is determined by its moral object), are two different fonts of morality. The deliberate frustration of the procreative meaning refers not to the intention (the intended end, or goal, or purpose), but to the deliberate (intentional) choice of any sexual act that is not, in and of itself, inherently procreative. Intrinsically evil acts are always deliberately (intentionally) chosen. The Magisterium has condemned every type of act that is intrinsically non-procreative, because act itself is not inherently ordered toward its proper moral object. All such acts are grave sins.