 A third objection is related. The view seems to involve a double standard in permitting infertile opposite-sex couples to marry (Corvino 2005; Macedo 1995). The new natural lawyers have responded that penile-vaginal sex is reproductive in type, even if not in effect, while same-sex activity can never be reproductive in type (Finnis 1997, cf. George 2000, Lee 2008). Reproductive-type sex can be oriented towards procreation even if not procreative in effect. But it is unclear how individuals who know themselves to be infertile can have sex for the reason of procreation (Macedo 1995, Buccola 2005). Ultimately, to differentiate infertile heterosexual couples from same-sex couples, new natural lawyers invoke complementarity between men and women as partners and parents. Thus, the defense of this account of marriage turns on a controversial view of the nature and importance of sexual difference (Finnis 1997, Lee 2008).