Why are homosexual acts always gravely immoral, and why is it simply impossible for persons of the same sex to marry? To answer these questions I will first review the teaching of the Church. I will then argue that human persons, by choosing to engage in homosexual acts, harm the great goods of marriage and of their own bodily capacity for the marital act as an act of self-giving which constitutes a communion of bodily persons—the good that Pope John Paul II calls the “nuptial meaning of the body.”  Since this argument’s intelligibility depends on a proper understanding of these great goods, I will prepare its way by considering the intrinsic goodness of marriage and the marital act. I will then conclude with an argument to show why it is simply not possible for persons of the same sex to marry.
I. RELEVANT MAGISTERIAL TEACHING
Magisterial teaching is found in the Catechism of the Catholic Church (1993), and three documents of the Congregation for the Doctrine of the Faith: the Vatican Declaration on Certain Questions of Sexual Ethics (Latin title: Persona humana) (1975); the letter on The Pastoral Care of the Homosexual Person (1986); and Considerations Regarding Proposals to Give Legal Recognition to Unions Between Homosexual Persons (2003).
1. The Catechism of the Catholic Church
No. 2357 declares: “homosexuality refers to relations between men and women who experience an exclusive or predominant sexual attraction toward persons of the same sex.” After noting that “its psychological genesis remains largely unexplained” it goes on to affirm that Sacred Scripture presents homosexual acts as “acts of grave depravity” (cf. Gen 19:1-29, Rom 1:24-27, 1 Cor 6.10, and 1 Tim 1.10), and that therefore tradition “has always declared that ‘homosexual acts are intrinsically disordered’ (cf. Persona humana, no. 8)” and “contrary to natural law” insofar as they “close the sexual act to the gift of life” and “do not proceed from a genuine affective and sexual complementarity.” Thus “under no circumstances can they be approved.” Here the Catechism indicates reasons why homosexual acts are immoral, it does not develop these reasons or attempt to show their truth.
No. 2358 states that persons who have deep-seated homosexual tendencies “do not chose their homosexual condition” and that for most “it is a trial.” Homosexual men and women “must be accepted with respect, compassion, and sensitivity. Every sign of unjust discrimination in their regard should be avoided. These persons are called to fulfill God’s will in their lives and, if they are Christians, to unite to the sacrifice of the Lord’s cross the difficulties they may encounter from their condition.”
2. Persona humana (December 27, 1975)
This document distinguishes between persons whose homosexual inclination is
”transitory” and homosexuals “who are definitively such because of some kind of innate instinct or a pathological condition judged to be incurable.” Referring to persons in the second category, it notes that some claim that since the tendency is “natural,” this “justifies… homosexual relations within a sincere communion of life and love, analogous to marriage, in so far as such homosexuals feel incapable of enduring a solitary life.” While maintaining that “homosexuals must certainly be treated with understanding and sustained in the hope of overcoming their personal difficulties,” it affirms that “no pastoral method can be employed which would give moral justification to these acts…for according to the objective moral order homosexual relations are acts which lack an essential and indispensable finality. In Sacred Scripture they are condemned as a serious depravity….” (no. 8).
This Declaration clearly distinguished the homosexual orientation or inclination from homosexual acts, deeming the later absolutely immoral, but it made no effort to give arguments based on reason to show why such acts are intrinsically immoral.
3. The Pastoral Care of the Homosexual Person (October 1, 1986)
This document provides a rather comprehensive examination of the issue. I will focus attention on the following topics considered in it: (1) mistaken interpretations of the Vatican Declaration on Certain Questions of Sexual Ethics (Persona Humana); (2) erroneous interpretations of Scripture and their correction; (3) further bases for Church's teaching; (4) critique of one argument to justify homosexual acts; and (5) the homosexual's vocation.
a. Mistaken Interpretations of Persona Humana
Persona Humana had distinguished between the homosexual condition and homosexual acts. But the Letter notes that in the years following "an overly benign interpretation was given to the homosexual condition itself, some going so far as to call it neutral or even good" (n. 3). To correct this, the Letter affirms that the homosexual inclination, while not a sin, "is a more or less strong tendency ordered toward an intrinsic moral evil and thus the inclination itself must be seen as an objective disorder" (no. 3; emphasis added). This assertion elicited very strong opposition and charges of homophobia. I suggest that we might consider the inclination as a specific manifestation of the concupiscence that comes from sin (original sin) and leads to sin but is itself not sin (see Council of Trent, Denzinger-Schoenmetzer, 1515), just as are inclinations to be violent or to drink to excess. 
b. Erroneous Interpretations of Scripture and Their Correction
The Letter identifies as one of the major causes of current confusion a "new exegesis of Sacred Scripture which claims variously that Scripture has nothing to say on the subject of homosexuality or that it somehow tacitly approves of it or that all of its moral injunctions are so culture-bound that they are no longer applicable to contemporary life" (no. 4).  The Letter declares that these views are "gravely erroneous" (no. 4). In correcting these views the Letter notes that, although many things have changed since the time the Scriptures were written, "there is nonetheless a clear consistency within the Scriptures themselves on the moral issue of homosexual behavior. The Church's doctrine regarding this issue is thus based not on isolated phrases for facile theological argument, but on the solid foundation of a constant biblical testimony." Moreover, "it is essential to recognize that the Scriptures are not properly understood when they are interpreted in a way which contradicts the Church's living tradition. To be correct, the interpretation of Scripture must be in accord with that tradition" (no. 5). The Letter then cites an important passage of Vatican II's Dogmatic Constitution on Divine Revelation, Dei Verbum, no. 10 affirming that sacred tradition, Sacred Scripture, and the magisterium of the Church are "so connected and associated that one of them cannot stand without the others" (no. 5). This is a key hermeneutical principle in Catholic theology. The Bible is the Church’s book; thus the Church has the competence to give an authoritative interpretation of Scripture, and in doing so the Church takes seriously into account the way that Scripture has been understood throughout the Catholic tradition.
The Letter then indicates the solid bases, within Scripture, for the Church's teaching: (a) the creation of man as male and female, meant to cooperate with God in giving life to new human persons; (b) the fall and resulting concupiscence (Gen 1); (c) the judgments on homosexual behavior found in the Sodom and Gomorrah story (Gen 19), Lev 18:22 and 20:13, the teaching of Paul in 1 Cor 6:9 and Rom 1:18-32, and finally the significance of 1 Tim 1:10 (no. 6).  It seems to me that the Letter offers a good presentation of the condemnation of homosexual behavior in Scripture, but obviously arguments based on Scripture are not very persuasive to persons who do not accept its authority. Consequently, the Letter also offers other bases for the Church’s teaching.
c. Further Bases for the Church's Teaching
The Letter affirms that the Church's teaching on homosexual acts is rooted in God's plan regarding the life-giving and loving union of man and woman in marriage. This entails that "only in the marital relationship [is] the use of the sexual faculty...morally good" (no. 7). From this it follows that "to choose someone of the same sex for one's sexual activity is to annul the rich symbolism and meaning, not to mention the goals, of the Creator's sexual design. Homosexual activity is not a complementary union able to transmit life; and so it thwarts the call to a life of that form of self-giving which the Gospel says is the essence of Christian living." Moreover, like every moral disorder, "homosexual activity prevents one's own fulfillment and happiness by acting contrary to the creative wisdom of God" (no. 7). This section of the Letter sketches the rational grounds that can be used to show why homosexual acts are not morally good; I hope to develop these grounds below.
d. Critique of an Argument Justifying Homosexual Acts
The Letter notes that one common argument given to justify homosexual acts is that homosexually oriented persons have no other choice than to act in a homosexual way because of their lack of freedom (no. 11). The Letter rejects this position because it is rooted in the "unfounded and demeaning assumption that the sexual behavior of homosexual persons is always and totally compulsive and therefore inculpable" (n. 11). It insists that homosexual persons have the freedom to choose whether or not to engage in homosexual acts; this pertains to the dignity of the homosexual person (no. 6). 
e. The Vocation of the Homosexual
The Letter maintains that homosexual persons are called "to enact the will of God in their life by joining whatever sufferings and difficulties they experience by virtue of their condition to the sacrifice of the Lord's cross." Self-denial is not pointless; "the cross is a denial of self, but in service to the will of God himself, who makes life come from death and empowers those who trust in him to practice virtue in place of vice" (no. 12). Homosexual persons, like all of us, are called to chastity (no. 12). 
4. Considerations Regarding Proposals to Give Legal Recognition to Unions Between Homosexual Persons (June 3, 2003)
These considerations, the Congregation states, “do not contain new doctrinal elements” but “seek rather to reiterate the basic points on this question and draw arguments from reason which could be used by bishops in preparing more specific interventions….The present considerations are also intended to give direction to Catholic politicians by indicating the approaches to proposed legislation in this area which would be consistent with Christian conscience” (no. 1).
Part I (nos. 2-4) summarizes the nature of marriage and its inalienable characteristics as a life-long union of one man and one woman open to the gift of children, a union elevated by Christ to the dignity of a sacrament. The CDF declares: “there are absolutely no grounds for considering homosexual unions to be in any way similar or even remotely analogous to God’s plan for marriage and family. Marriage is holy, while homosexual acts go against the natural moral law….and ‘close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity…” (no. 4, internal citation from The Catechism of the Catholic Church, no. 2357).
Part II (no. 5) considers positions on the problem of homosexual union—toleration, advocating legal recognition, giving such unions legal equivalence to marriage along with the legal possibility of adopting children. If the government’s policy is de facto tolerance with no explicit recognition of homosexual unions, moral conscience “requires that…Christians give witness to the whole moral truth, which is contradicted both by approval of homosexual acts and unjust discrimination against homosexual persons.” Prudent actions that can be effective include “unmasking the way in which such tolerance might be exploited or used in the service of ideology; stating clearly the immoral nature of these unions; reminding the government of the need to contain the phenomenon within certain limits so as to safeguard public morality and, above all, to avoid exposing young people to erroneous ideas about sexuality and marriage….” If such unions have been given legal recognition or the rights and status of marriage, “clear and emphatic opposition is a duty.”
Part III (nos. 6-9) sets forth arguments from reason against legal recognition of homosexual unions. First, in an argument from the order of right reason the CDF answers those who ask how a law can be contrary to the common good if it simply gives legal recognition to a de facto reality which does not seem to cause injustice to anyone. Its reply: “One needs first to reflect on the difference between homosexual behavior as a private phenomenon and the same behavior as a relationship in society, foreseen and approved by law, to the point where it becomes one of the institutions in the legal structure. The second phenomenon is not only more serious but also assumes a more wide-reaching and profound influence and would result in changes to the entire organization of society, contrary to the common good….Legal recognition of homosexual unions would obscure certain basic moral values and cause a devaluation of the institution of marriage” (no. 6).
Considering the matter from the biological and anthropological order the CDF says that homosexual unions are:
totally lacking in the biological and anthropological elements of marriage and family which would be the basis, on the level of reason, for granting them legal recognition. Such unions are not able to contribute in a proper way to the procreation and survival of the human race…Homosexual unions are also totally lacking in the conjugal dimension, which represents the human and ordered form of sexuality. Sexual relations are human when and insofar as they express and promote the mutual assistance of the sexes in marriage and are open to the transmission of new life….the absence of sexual complementarity in these unions creates obstacles in the normal development of children who would be placed in care of such persons. They would be deprived of the experience of either fatherhood or motherhood. Allowing children to be adopted by persons living in such unions would actually mean doing violence to these children, in the sense that their condition of dependency would be used to place them in an environment that is not conducive to their full human development (no. 7).
Here the CDF has clearly indicated reasons why homosexual acts are immoral and why homosexual unions ought not to be equated with marriage. The reasons given, however, need to be explained more thoroughly.
Considering the issue from the social order, the CDF holds that society owes its continued survival to the family founded on marriage, and that the inevitable consequence of legalizing homosexual unions “would be the redefinition of marriage, which would become…an institution devoid of essential reference to factors linked to heterosexuality; for example, procreation and raising children….the concept of marriage would undergo a radical transformation, with detriment to the common good” (no. 8).
Considering the issue from the legal orde,r the CDF argues that married couples, because they ensure the succession of generations, are “eminently within the public interest and therefore civil law ought to grant their marriages institutional recognition. “Homosexual unions, on the other hand, do not need specific attention from the legal standpoint since they do not exercise this function for the common good” (no. 8). It seems to me that this is a very important argument against regarding homosexual unions as marriages; however, it needs to be more fully explained and developed.
Then, in a very important passage the CDF declares: “Nor is the argument valid according to which legal recognition of homosexual unions is necessary to avoid situations in which cohabiting homosexual persons, simply because they live together, might be deprived of real recognition of their rights as persons and citizens. In reality, they can always make use of the provisions of law…to protect their rights in matters of common interest. It would be gravely unjust to sacrifice the common good and just laws on the family in order to protect personal goods that can and must be guaranteed in ways that do not harm the body of society” (no. 9).
This passage is most important. It recognizes that it is morally permissible to concede to households formed by individuals who are indeed of the same sex (male or female) various civil rights not because of any sexual relationship but rather on the basis that they form a valid kind of economic/social household built on friendship, e.g., two widows or widowers, a son and his elderly father, a daughter and her elderly widowed mother etc. who choose to live together for purposes of friendship and of economy. It is worth noting that an arrangement of this kind to meet the just demands of non-traditional, i.e., non-familial, households, had been arranged in 1997 in San Francisco when some sought to coerce the Archdiocese of San Francisco to grant such civil rights to households rooted in the sexual orientation and sexual relationship of its members, i.e., same sex couples united in their desire to engage in acts of sodomy. This effort was successfully thwarted by recognizing the just civil demands of households formed by persons of the same sex for purposes of economic stability and common friendship and not for the purpose of engaging in non-marital sexual acts (for this see http://www.cwnews.com/news/viewstory.cfm?recnum=4248).
Part IV (no. 10) takes up the positions of Catholic politicians regarding legislation in favor of homosexual unions. I omit this part.
II. WHY ARE HOMOSEXUAL ACTS ALWAYS GRAVELY IMMORAL?
Centuries ago, St. Thomas declared: “we offend God only by acting contrary to our own good,”  and Pope John Paul II instructs us that “the commandments of which Jesus reminds the young man are meant to safeguard the good of the person, the image of God, by protecting his goods” (Encyclical Veritatis splendor, no. 13; emphasis in original). From this it follows that if homosexual acts are gravely immoral they are so because they harm the good(s) of human persons. But what good or goods? As I noted in the introduction, the goods harmed by such acts are the goods of marriage and of the body’s capacity for the marital act as an act of self-giving which constitutes a communion of bodily persons--what Pope John Paul II calls the “nuptial meaning of the body.” First, however, it is necessary to show that the marriage of a man and a woman is intrinsically, not instrumentally, good and that the marital act, whereby they give themselves to one another, honors this good and the “nuptial meaning of the body.”
1. Marriage, an Intrinsic, Fundamental Human Good, and the Marital Act
St. Augustine explicitly held that marriage is only an instrumental good, in the service of the procreation and education of children so that the intrinsic, non-instrumental good of friendship of fathers with their sons will be realized by the propagation of the race and the intrinsic good of inner integration be realized by “remedying” the disordered desires of concupiscence. Had Augustine integrated the natural or companionship of the spouses into his understanding of marriage, he would, as John Finnis has noted, have recognized that in both sterile and fertile marriages “the communion, companionship, societas and amicitia of the spouses—their being married—is the very good of marriage and is an intrinsic, basic human good, not merely instrumental to any other good.”  Vatican Council II clearly indicated this great truth, for it teaches that “God did not create the human person as a solitary,” and after citing “male and female he created them” (Gn 1.27) explains that the two sexes’ “companionship produces the primary form of interpersonal communion. For, by their innermost nature human beings are social, and unless they relate themselves to one another they can neither live nor develop their gifts.”  As Germain Grisez says, in commenting on this passage, “This gloss on Gn 1.27 implies that marriage is not merely an instrumental good: the companionship of man and woman belongs to humankind as image of God and is the primary form of one of the essential, intrinsic aspects of human fulfillment.  That marriage is a basic good is central to the teaching of Pope John Paul II. In Familiaris consortio, no. 11, he identifies marriage as one way of realizing the human vocation to love and in Mulieris dignitatem, no. 7, declares that the communio personarum of husband and wife is an image of the Trinitarian communio personarum of Father, Son, and Holy Spirit. In Veritatis splendor he explicitly refers to the communion of persons in marriage as a fundamental human good in no. 13, and it is evident that he includes this basic good among the other goods of the human person that must be respected and honored in every choice in nos. 48, 50, and 67. Moreover, as Finnis points out,
The Church often speaks of the goods of marriage: (1) loving friendship between wife and husband, and (2) procreating and educating any children who may be conceived from the spouses’ marital intercourse [see, e.g., Catechism of the Catholic Church, nos. 2201, 2249]. They are interdependent goods…Being interdependent, these goods can also be properly described as two aspects of a single, basic human good, the good of marriage itself. In the Church’s most explicit teaching on the foundations of its moral doctrine [Veritatis splendor], in which Pope John Paul II points to the basic human goods as the first principles of the natural moral law, this single though basic good is called: ‘the communion of persons in marriage’ [no. 13]. 
Marriage is consummated by the marital act, which is far more than a genital act between a man and a woman who happen to be married. Men and women are capable of having genital sex because they have genitals, and thus fornicators and adulterers are able to have genital sex. But fornicators and adulterers are not capable of engaging in the conjugal or marital act precisely because they are not married, and it is marriage that capacitates spouses to engage in the marital act, i.e., to do what spouses are supposed to do, to become literally one flesh in an act whereby the man personally gives himself to his wife by entering into her body person, and in doing so receives her and whereby the woman personally receives her husband into her body person and by doing so gives herself to him. The husband gives himself to his wife in a receiving way, while she receives him in a giving way. The conjugal or marital act actually unites two persons who have made each other irreplaceable, non-substitutable, and non-disposable in their lives by giving themselves to one another and receiving one another in marriage. The marital act, consequently, is the kind or type of act intrinsically fit or apt both for communicating conjugal love and for receiving the gift of life if the couple is fertile. 
In short, marriage, considered as a two-in-one-flesh communion of persons consummated and actualized by the marital act, which is an act open to the blessings or goods of marriage—faithful conjugal love and the gift of children-- is an intrinsic or basic human good and as such provides a non-instrumental reason for spouses to engage in the marital act. 
This act is and remains a procreative or reproductive kind of act even if the spouses, because of non-behavioral factors over which they have no control, for example, the temporary or permanent sterility of one of the spouses, are not able to generate human life in a freely chosen marital act. Their act remains the kind of bodily act that alone is “apt” for generating human life. As Robert George and Gerard V. Bradley note in answer to a homosexual apologist’s question regarding the point of sex in an infertile marriage: “the intrinsic point of sex in any marriage, fertile or not, is…the basic good of marriage itself, considered as a two-in-one-flesh communion of persons that is consummated and actualized by acts of the reproductive type. Such acts alone among sexual acts can be truly unitive, and thus marital, and marital acts, thus understood, have their intelligibility and value intrinsically, and not merely by virtue of their capacity to facilitate the realization of other goods.” 
Pope John Paul II has written perceptively of the “language of the body” and the way in which the marital act speaks this language. His thought on this matter is nicely summarized in the following passage from Donum vitae, the 1987 Vatican Instruction on Respect for Human Life in Its Origins and on the Dignity of Human Procreation:
Spouses mutually express their personal love in the ‘language of the body,’ which clearly involves both ‘spousal meanings’ and parental ones. The conjugal act by which the couple mutually expresses their self-gift at the same time expresses openness to the gift of life. It is an act that is inseparably corporal and spiritual. It is in their bodies and through their bodies that the spouses consummate their marriage and are able to become father and mother. 
The following passage from Finnis can serve to bring this section to a close:
The union of the reproductive organs of husband and wife really unites them biologically (and their biological reality is part of, not merely an instrument of, their personal reality); reproduction is one function and so, in respect of that function, the spouses are indeed one reality, and their sexual union can actualize and allow them to experience their real common good—their marriage with the two goods, parenthood and friendship, which (leaving aside the order of grace) are the parts of its wholeness as an intelligible common good even if, independently of what the spouses will, their capacity biological parenthood will not be fulfilled by that act of genital union. 
2. Homosexual Acts Damage the Goods of Marriage and of the Nuptial Meaning of the Body.
Homosexual couples can surely live in a committed relationship with sincere mutual affection and express this affection in ways appropriate for any friendship. Moreover, as we saw in reviewing the Church’s teaching, such couples, as forming an economic unit, have a just claim to benefits that can be granted to other same-sex couples living together, for instance, widows or widowers. Such couples might claim that they cannot satisfy their sexual urges and natural inclination toward intimate union in any more adequate way than by establishing a more or less permanent relationship that includes sexual intimacy, and that one appropriate way for them to express their affection and friendship is to engage in homosexual acts.  Homosexual acts in the strict sense are anal or oral intercourse willingly engaged in by two males, with the intention that at least one of them achieve satisfaction by ejaculating within the other’s body. Such acts are acts of sodomy or homosexual intercourse. A lesbian couple can, without engaging in intercourse, stimulate each other to orgasm, and such intentional acts can also be regarded as homosexual in a broader sense. And both male and female homosexuals may choose to masturbate each other as ways of expressing their affection. But are such acts the right means to choose to do so? Are they truly “appropriate”? To settle whether they are requires us to examine these acts and what they do to the persons choosing them.
Before giving a moral analysis of these acts it seems to me helpful to describe in some detail the physiology of one specific homosexual act, namely, anal intercourse, the sine qua non for many male homosexuals.  However, human physiology, as John R. Diggs, Jr., M.D., points out,
makes it clear that the body was not designed to accommodate this activity. The rectum is significantly different from the vagina with regard to suitability for penetration by a penis. The vagina has lubricants and is supported by a network of muscles. It is composed of a mucus membrane with a multi-layer stratified squamous epithelium that allows it to endure friction without damage and to resist the immunological actions caused by semen and sperm. In comparison, the anus is a delicate mechanism of small muscles that comprise an “exit-only” passage. With repeated trauma, friction, and stretching, the sphincter loses its tone and its ability to maintain a tight seal. Consequently, anal intercourse leads to leakage of fecal material that can easily become chronic. The potential for injury is exacerbated by the fact that the intestine has only a single layer of cells separating it from highly vascular tissue, that is, blood. Therefore, any organisms that are introduced into the rectum have a much easier time establishing a foothold for infection than they would in a vagina….Furthermore, ejaculate has components that are immunosuppressive. In the course of ordinary reproductive physiology, this allows the sperm to evade the immune defenses of the female….The end result is that the fragility of the anus and rectum, along with the immunosuppressive effect of ejaculate, make anal-genital intercourse a most efficient manner of transmitting HIV and other infections. The list of diseases found with extraordinary frequency among male homosexual practitioners as a result of anal intercourse is alarming: anal cancer, chlamydia trachomatis, cryptosporidium, giardia lamblia, herpes simplex virus, human immunodeficiency virus, human papilloma virus, isospora belli, microsp;oridia, gonorrhea, viral hepatitis type B & C, syphilis. 
I thought it relevant to cite this long passage because it gives reasons to show that anal sex is hardly an appropriate way to express friendship. However, it does not get to the heart of the reason why the choice to engage in homosexual acts damages the nuptial meaning of the body and the good of marriage. I will now offer an argument to show this.
Patrick Lee and Robert George articulate a claim central to this argument: “if one chooses to actualize one’s bodily, sexual power as an extrinsic means of producing an effect in one’s consciousness, then one separates in one’s choice oneself as bodily from oneself as an intentional agent. The content of such a choice includes the dis-integration attendant upon a reduction of one’s bodily self to the level of an extrinsic instrument.”  When one treats one’s body as intrinsic to one’s self, there is a unitary activity, and various bodily actions share in this activity since they are not directed to an extrinsic purpose. In activity of this kind one is freely choosing to instantiate real goods, e.g., the good of play in basketball or the good of health in exercising or the good of friendship in writing a letter or in conversing, and one’s efforts to realize those goods involve, where appropriate, one’s bodily activity so that, as Finnis says, “that activity is as much the constitutive subject of what one does as one’s act of choice is.”  Thus in the marital act, spouses freely choose to instantiate their communion of persons in one flesh open to the gift of life in and through an act in which their bodily activity is as much the constitutive subject of what they are doing as is their act of choice.
However, in sodomitical and other kinds of homosexual behavior, the joining of the bodies of the persons of the same sex is not such that they become one complete organism. The bodies of persons engaging in homosexual acts do not contribute to a communio personarum. Although they may choose such acts as means of experiencing personal intimacy, the resulting experience cannot be the experience of any real unity between them. Rather, as Grisez has put it so accurately, “each one’s experience of intimacy is private and incommunicable, and no more a common good than is the mere experience of sexual arousal and orgasm. Therefore, the choice to engage in sodomy for the sake of that experience of intimacy in no way contributes to the partners’ real common good as committed friends.”  Thus persons choosing homosexual acts choose to use their own and each other’s bodies to provide subjective satisfactions, states of consciousness. Thus the body becomes an instrument used and the conscious subject the user. The conscious self is alienated from the body, resulting in an existential dualism between the body and the conscious subject, i.e., “a division between the two insofar as they are co-principles of oneself considered as an integrated, acting, sexual person.” Therefore, to choose to engage in homosexual acts is to choose a specific kind of self-disintegrity. The self-integration damaged in this way is the unity of the acting person as conscious subject and sexually functioning body. But, as Grisez continues, “this specific aspect of self-integration…is precisely the aspect necessary so that the bodily union of sexual intercourse will be a communion of persons, as marital intercourse is.” Therefore, homosexual acts damage “the body’s capacity for the marital act as an act of self-giving which constitutes a communion of bodily persons,” or in other words, the “nuptial meaning of the body”. 
Homosexual acts, consequently, damage the good of the body’s capacity for self-gift, its nuptial meaning. Such acts, moreover, are ones in which those engaging in them do not even encounter each other face-to-face, a uniquely human way of copulating, but rather in a way characteristic of sub-human animals. Because homosexual acts damage the nuptial meaning of the body, they also damage the good of marriage itself. They do so because the great good of marriage requires that spouses recognize that their bodies are integral to their being as persons and that it is precisely their sexual complementarity, revealed in their bodily differences, that makes it possible for the man to “give himself in a receiving way” to his wife in the marital act and for his wife “to receive him in a giving way” in this same act, an act having two common subjects.
III. An Argument Against Same-Sex Marriage
Persons of the same sex cannot marry because they cannot do what married couples can do, i.e., to consummate their union by a bodily act in which they become the common subjects of an act that, precisely as human behavior, is eminently fit both for the communication of spousal love and for the generation of new human life.
The spousal union goes beyond biological union, but biology is an essential component. By their marital acts husband and wife express in a profound way their whole married life together: two-in-one-flesh. When those acts bear the fruit of children, the latter literally issue from the marital union: they embody this union and extend it in space and time.
Genital coition is the only bodily act intrinsically capable of generating new human life. Kissing, holding hands, fondling, and anal/oral sex cannot generate children. They can be generated through acts of fornication and adultery, but it is not good for children to be begotten in this way. For millennia every human culture has recognized the bond linking sex, marriage, and the generation of human life and frowned on begetting children out of wedlock. Although many today think it fitting to generate children outside of marriage, the tragic situations accompanying phenomena such as fatherless children, undisciplined youth, and abandoned women show the shallowness of such thinking.
Our society, as any society, can survive only if new human persons are generated. The marital union of a man and a woman who have given themselves unreservedly in marriage and who can consummate their union in a beautiful bodily act of conjugal intercourse is the best place to serve as a “home” for new human life, as the “place” where this life can take root and grow in love and service to others. A marriage of this kind contributes uniquely to the common good. It merits legal protection; same-sex unions are not the same and sadly merely mimic the real thing. They can in no way be regarded as marriages in the true sense.
* This essay is copyrighted 2004 by the National Catholic Bioethics Quarterly and is reproduced here with its permission.
1. On the nuptial meaning of the body see John Paul II, The Theology of the Body: Human Love in the Divine Plan (Boston: Pauline Books and Media, 1997), General Audience of January 9, 1980, :“The Nuptial Meaning of the Body,” pp. 60-63.
2. On this see John Finnis, “’An Intrinsically Disordered Inclination,” in Same-Sex Attraction: A Parents’ Guide, ed. John F. Harvey, OSFS, and Gerard V. Bradley (South Bend, IN: St. Augustine’s Press, 2003), pp. 89-99.
3. The following works illustrate these views: Human Sexuality: New Directions in American Catholic Thought, eds. Anthony Kosnik, William Carroll, Agnes Cunningham, Ronald Modras, and James Schulte (New York: Paulist, 1977), pp. 186-196; Daniel Maguire, “The Morality of Homosexual Marriage,” in Challenge to Love: Gay and Lesbian Catholics in the Church, ed. Robert Nugent (New York: Crossroads, 1983), John J. McNeill, The Church and the Homosexual (Kansas City: Sheed, Ward, and McMeel, 1976), pp. 37-66.
4. Sound studies of the biblical teaching on the immorality of homosexual acts are the following: Silverio Zedda, S.J., Relativo e assoluto nella morale di San Paolo (Brescie: Paideia Editrice, 1984), ch. 5, on the teaching of St. Paul; Manuel Miguens, O.F.M., “Biblical Thoughts on ‘Human Sexuality,’” in Human Sexuality in Our Time, ed. George A. Kelly (Boston: Daughters of St. Paul, 1979), pp. 102-119; Joseph Jensen, O.S.B., “The Relevance of the Old Testament,” in Dimensions of Human Sexuality, ed. Denis Doherty (New York: Doubleday, 1979), chapter 1; Kevin E. Miller, “Scripture and Homosexuality,” in Same-Sex Attraction, pp. 53-74.
5. The argument repudiated is in essence the one used frequently by Charles E Curran to justify homosexual acts under certain conditions. See his “Dialogue with the Homophile Movement: The Morality of Homosexuality,” in his Catholic Moral Theology in Dialogue (Notre Dame, IN: Fides, 1972) pp. 184-219.
6. John F. Harvey, O.S.F.S., has done wonderful work in developing a program, modeled in some ways on Alcoholics Anonymous, to help homosexually oriented persons live chaste lives. His founded the spiritual support group, Courage, to achieve this goal. He describes Courage and its work in his books The Homosexual Person (San Francisco: Ignatius Press, 1987), pp. 137-161, and The Truth About Homosexuality: The Cry of the Faithful (San Francisco: Ignatius Press, 1996), pp. 19-30.
7. I acknowledge here my indebtedness to the work of Germain Grisez, John Finnis, Robert George and Gerard V. Bradley, Robert George and Patrick Lee on this matter. See Grisez’s Living a Christian Life (Quincy, IL: Franciscan Press, 1993), pp. 648-656; John Finnis, “Personal Integrity, Sexual Morality and Responsible Parenthood,” Anthropos: Rivista sulla Persona e la Famiglia 1.1 (1985) 43-55; “Law, Morality, and ‘Sexual Orientation,’” Notre Dame Law Review 69 (1994) 1049-1076; “The Good of Marriage and the Morality of Sexual Relations: Some Philosophical and Historical Observations,” American Journal of Jurisprudence 42 (1997) 97-134; Robert George and Gerard V. Bradley, “Marriage and the Liberal Imagination,” Georgetown Law Journal 84 (1995) 301-320; Robert George and Patrick Lee, “What Sex Can Be: Self-Alienation, Illusion, or One-Flesh Union,” American Journal of Jurisprudence 42 (1997) 135-150.
8. St. Thomas Aquinas, Summa contra gentiles, Bk. 3, ch. 122: “Non enim Deus a nobis offenditur nisi ex eo quod contra nostrum bonum agimus.”
9. John Finnis, “Law, Morality, and ‘Sexual Orientation,’” 1064-1065.
10. Vatican Council II, Pastoral Constitution on the Church in the Modern World (Gaudium et spes), no. 12
11. See Living a Christian Life, p. 557, footnote 5. Moreover, Gaudium et spes speaks of marriage as “a community of love” (no. 48) and indeed as an “intimate community of conjugal life and love” (no. 49).
On marriage as a fundamental or basic good see Grisez, pp. 553-569.
12. Finnis, “’An Intrinsically Disordered Inclination,’” p. 93. In a note to this passage, note 20, p. 99, Finnis adds: “St. Thomas Aquinas long ago identified this as a single though complex primary (basic) human good: see John Finnis, Aquinas: Moral, Political, and Legal Theory (Oxford: Oxford University Press, 1998), 82, 143.”
13. On this see my essays, “La ‘communio personarum’ e l’atto coniugale,” in Morale coniugale e sacramento della Penitenza: Riflessioni sul “Vademecum per i confessori” (Città del Vaticano: Libreria Editrice Vaticana, 1998), pp.135-150; “Marriage and the Complementarity of Male and Female,” in my Marriage: The Rock on Which the Family Is Built (San Francisco: Ignatius Press, 1995), pp. 48-49. See also Robert Joyce, Human Sexual Ecology: A Philosophy of Man and Woman (Washington, D.C.: University Press of America, 1980), pp. 63-85. It is precisely because the conjugal or marital act is, qua marital, open to the blessings of marriage that Vatican Council II declared: “Married love is uniquely expressed and perfected by the exercise of the acts proper to marriage. Hence the acts in marriage by which the intimate and chaste union of the spouses takes place are noble and honorable; the truly human performance of these acts fosters the self-giving they signify and enriches the spouses in joy and gratitude” (Gaudium et spes, no. 48).
14. See Robert George and Gerard V. Bradley, “Marriage and the Liberal Imagination,” 301-302.
15. Ibid, 305. They are answering an objection posed by Stephen Macedo, “Homosexuality and the Conservative Mind,” Georgetown Law Journal 84 (1995) 278.
16. Congregation for the Doctrine of the Faith, Donum vitae, II, B 4b.
17. Finnis, “Law, Morality, and ‘Sexual Orientation’,” 1066.
18. See, for instance, Steven Macedo, “Sexuality and Liberty: Making Room for Nature and Tradition?” in Sex, Preference, and Family: Essays on Law and Nature, ed. David M. Estlund and Martha Nussbaum (New York: Oxford University Press, 1977), pp. 86-101, at pp. 90-97 .
19. Gabriel Rotello, Sexual Ecology: AIDS and the Destiny of Gay Men (New York: Penguin, 1998), p. 92. Note that Rotello is himself an active homosexual.
20. John R. Diggs, Jr. M.D., “The Health Risks of Gay Sex,” Corporate Resource Council paper copyright 2002, p. 3. In note 25, p. 12 Diggs provides the scientific sources for the list of diseases associated with anal intercourse: Anne Rompalo, “Sexually Transmitted Causes of Gastrointestinal Symptoms in Homosexual Men,” Medical Clinics of North America 74(6: 1633-1645 (November 1990); “Anal Health for Men and Women,” LGBTHealthChannel, www.gayhealthchannel.com/analhealth/; “Safer Sex (MSM) for Men Who Have Sex with Men,” LGBTHealthChannel, www.gayhealthchannel.com/stdmsm/.
21. Patrick Lee and Robert George, “What Sex Can Be: Self-Alienation, Illusion, or One-Flesh Union,” 139.
22. Finnis, “Personal Integrity, Sexual Morality, and Responsible Parenthood,” 46.
23. Grisez, Living a Christian Life, p. 653.
25. Ibid, p. 650. At this point in his text Grisez is specifically addressing masturbation, but the analysis applies to homosexual acts as well.
*This paper is reproduced with the permission of the National Catholic Bioethics Quarterly.
Copyright ©; National Catholic Bioethics Quarterly 2004
Version: 31st August 2004