 A normative argument for that marriage is essentially different-sex appeals to its purpose: reproduction in a naturally procreative unit (see 3.2.a). But marriage does not require that spouses be able to procreate naturally, or that they intend to do so at all. Further, married couples adopt and reproduce using donated gametes, rather than procreating ‘naturally’. Nor do proponents of this objection to same-sex marriage generally suggest that entry to marriage should be restricted by excluding those unable to procreate without third-party assistance, or not intending to do so.