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A Defense of the ‘Sterility Objection’ to the New Natural Lawyers’ Argument Against Same-Sex Marriage


The “new natural lawyers” (NNLs) are a prolific group of philosophers, theologians, and political theorists that includes John Finnis, Robert George, Patrick Lee, Gerard Bradley, and Germain Grisez, among others. These thinkers have devoted themselves to developing and defending a traditional sexual ethic according to which homosexual sexual acts are immoral per se and marriage ought to remain an exclusively heterosexual institution. The sterility objection holds that the NNLs are guilty of making an arbitrary and irrational distinction between same-sex couples and sterile heterosexual couples. The NNLs believe that it is a necessary condition for two people’s being morally and legally entitled to get married that they be able to perform sexual acts that are “suited to procreating.” But sterile heterosexual couples are incapable of performing such acts. Therefore, it should follow from the NNLs’ own premises that sterile heterosexual couples are not entitled to marry. But the NNLs do not draw this conclusion. Instead, they maintain that sterile heterosexuals can marry while denying that the same is true of same-sex couples. The sterility objection claims the NNLs are being inconsistent in treating the two kinds of couples differently. Although the sterility objection has been endorsed by recent critics, I don’t think it has yet been adequately defended. The NNLs have responded by arguing that there is a sense in which the sex acts of sterile heterosexual couples are as suited to reproduction as those of fertile heterosexuals. Thus they maintain that the distinction they draw between the two kinds of couple has a rational basis. A successful defense of the sterility objection must show that this response on the part of the NNLs fails. Such is the task I undertake in this paper. I argue that the NNLs’ response fails because acts of penile-vaginal intercourse between sterile heterosexuals lack the actual causal power to produce conception that sexual acts need to be considered truly reproductive, and because their assumption that penile-vaginal intercourse always functions reproductively is bad biology.

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  1. 1.

    The label ‘the sterility objection’ appears to come from Weithman (1997: 238), although he himself does not defend the objection.

  2. 2.

    Finnis (1997: 100, note 11) endorses Lee and George’s focus on “inner integrity” as a basic human good in their version of the argument against homosexual conduct (reprinted in George 1999: 161–183). The conception of practical reasonableness that he attributes to Aquinas seems already to include the good of self-integration within it (Finnis 1998: 83–84).

  3. 3.

    The practical principles directing us to pursue the basic human goods “take the form: Such and such a basic human good is to be done and/or pursued, protected, and promoted” (Grisez 1983a: 180). They are all “determinations” of a more basic first principle of practical reason that is also held to be self-evident: “Good is to be done and pursued” (Grisez 1983a: 180; cf. Grisez et al. 1987: 119–120).

  4. 4.

    The first principle of morality is supposed to be self-evident, although the intermediate moral principles that “specify” it are not (George 1999: 44, 52).

  5. 5.

    Thus marriage includes the kind of “true friendship” that Finnis, in a discussion influenced by Aristotle, distinguishes from relationships between business associates and relationships devoted to the good of “play” (1980: 139–144). True friends value each other for their own sake, value acting together for its own sake, and see their well-being as inextricably bound up with the well-being of their friend. For a revision of new natural law theory that rejects the idea of marriage as a basic human good and tries to see marriage as simply a form of friendship, see Goldstein (2011).

  6. 6.

    Indeed, the NNLs think that men and women are not just biologically complementary—they are “emotionally, psychologically, and spiritually” complementary as well (Lee and George 2008: 201). Their belief in the existence of a robust set of essential gender differences is part of a relatively neglected aspect of their conception of marriage: its patriarchal nature. According to Grisez, the “husband-father” is to deal “with the wider world outside the home in order to obtain the necessities of life and defend his family against threats to its security” while the “wife-mother” is to “[nurture] her children for many years” (1993: 627–628). In certain circumstances, the husband has the authority to make decisions for his wife and family, to which the latter should “submit” (629–632). He further declares the two sexes to be “naturally adapted” to these roles. The patriarchal aspects of traditional marriage are relatively muted in the writings of Finnis, Lee, and George; it seemed as though the NNLs would get a free pass on the issue until the publication of Nicholas C. Bamforth and David A. J. Richards (2008), which addresses it at length (see especially 232–236).

  7. 7.

    Acts of penile-vaginal intercourse are taken to be biologically unifying only if they are taken to “completion,” i.e. to the point of “ejaculation by the male in the female’s vagina” (Grisez 1993: 641). The NNLs hold that all such acts of penile-vaginal intercourse are biologically unifying, but they do not hold that all such acts are morally good. Cases of rape and pre- or extra-marital sex can be genuinely biologically unifying without being morally good. Rather, only those complete acts of penile-vaginal intercourse that occur in the context of marriage and are engaged in for the sake of the marriage itself are morally good.

  8. 8.

    The NNLs do include what we might think of as a “foreplay exception” for married heterosexual couples: acts other than penile-vaginal intercourse (e.g. manual stimulation) are permissible as foreplay, but cannot be substituted for the main event (Grisez 1993: 641). In a move that seems truly ad hoc, Grisez also allows that while a woman’s orgasm is “not necessary for sexual intercourse insofar as it is a reproductive function,” acts that are intended to bring her to orgasm—even those that are done “during foreplay or after the husband’s ejaculation and withdrawal”—are permissible as long as they are “continuous” with a “complete act of marital intercourse” (642).

  9. 9.

    I note an apparent consequence of the NNLs’ argument that many readers will find unpalatable: heterosexuals who suffer from disabilities that make it impossible for them to perform acts of penile-vaginal intercourse would also be incapable of marriage and should apparently be barred from legally marrying. This thought was prompted by Perry (1995: 54–55) and Lawrence (2007). See also Salzman and Lawler (2006: 187).

  10. 10.

    One might respond to the foregoing arguments by holding that the members of a same-sex couple have a perfectly good reason for engaging in sexual acts, namely to share sexual pleasure with one another. In response, the NNLs would deny that sexual pleasure—or pleasure in general, for that matter—is by itself a good reason for action (George 1999: 149; Lee and George 2008: 186–187).

  11. 11.

    Gareth Moore (2000: 224–226; 2003: 253–257) is the main source for this objection.

  12. 12.

    The general principle invoked by the NNLs—that when sexually-reproducing organisms mate they become a single biological entity—may also have absurd consequences when applied beyond the case of humans and other mammals: perhaps the birds and the bees and the flowering plants they help pollinate are all a single organism? Or perhaps the birds and the bees are merely “organs” of a single organism composed by the flowering plants? The NNLs sometimes limit the principle to mammals (e.g. George 1999: 175) but that seems an arbitrary limitation.

  13. 13.

    Responses are found in Finnis (1995, 1997), George (1999), and Lee and George (2008). While these works follow and respond to the sterility objection as presented in Macedo (1995) and Koppelman (1997, 2002), the main elements of their response are already present in Grisez (1993).

  14. 14.

    Moore ascribes to Aquinas the view that “some acts have a purpose in themselves, regardless of the purpose of the agent; that is, they are of themselves ordered to an end” (2003: 217). The NNLs’ see reproduction as constituting the objective purpose of acts of penile-vaginal intercourse in this sense.

  15. 15.

    Natalie Angier has stressed the difficulties of conceiving even when a woman is fertile: “A woman is fertile only 5 or 6 days a month. … [E]ven if our hypothetical Don Juan hits a day on which a woman is ovulating, the chances are around 65 % that his sperm will fail to fertilize her egg; human reproduction is complicated, and most eggs and sperm are not up to the demands of proper fusion” (1999: 368). The evolutionary psychologists Randy Thornhill and Steven W. Gangestad cite an estimate that “the mean likelihood of conception resulting from a single episode of unprotected, consensual human copulation” is “a mere 2–4 %” (2008: 38).

  16. 16.

    “Most other animal species confine sex to a brief estrous period around the advertised time of ovulation. … We humans, though, practice sex on any day of the estrus cycle. Women solicit it on any day, and men perform without being choosy about whether their partner is fertile or ovulating. … Hence most human copulations involve women who are unable to conceive at that moment. Not only do we have sex at the ‘wrong’ time of the cycle, but we continue to have sex during pregnancy and after menopause, when we know for sure that fertilization is impossible” (Diamond 1997: 64–65).

  17. 17.

    “Nonprocreative sex is seemingly everywhere and everything. So much so that it is easier to define by negation: ‘nonprocreative sex’ encompasses those sexual activities that cannot result in conception. Nonprocreative sex runs the gamut from infantile and prepubescent sexual explorations to postmenopausal and infertile geriatric sex. Sex at the wrong time of the month, or with a partner rendered permanently infertile, is also nonprocreative, as is sex that employs effective methods of contraception, including condoms, diaphragms, and ‘the pill.’ Homosexual sex is clearly nonprocreative, but so are many of the activities in which heterosexuals engage, including masturbation, oral sex, anal intercourse, and yes, even passionate kissing” (Abramson and Pinkerton 2002: 17–18).

  18. 18.

    I would like to thank Jack Mulder, J. Aaron Simmons, and two anonymous reviewers for their extremely helpful comments on this paper.


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Correspondence to Erik A. Anderson.

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Anderson, E.A. A Defense of the ‘Sterility Objection’ to the New Natural Lawyers’ Argument Against Same-Sex Marriage. Ethic Theory Moral Prac 16, 759–775 (2013).

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  • Homosexuality
  • New natural law
  • Same-sex marriage
  • Sexual ethics
  • Gay rights