In this lecture, John Haldane discusses the incoherent and schizophrenic understanding of sex and sexuality in modern society. He also addresses the sentimentalization and infantilization of our understanding of sex and illustrates this by reference to the argument that presently underpins the push for a redefinition of marriage. he calls this, Argumentum ad Consummationem, and he argues that it depends upon two premises, the first of which is that sexual attraction and love are the determinants of human happiness and should be consummated where sincerely felt, and the second, you cannot choose to whom you are sexually attracted, and you cannot choose to whom you fall in love, that combined lead to the conclusion, therefore, whether or not they are chosen, attraction and love should be consummated where they are sincerely felt. If this is the animating principle of the marriage revisionist movement, and I think it is, than as I have argued elsewhere, and as Haldane argues here, there can be no objection to incestuous marriage, or polyamorous marriage, leave alone gay marriage, or any other combination of marriage once we move beyond natural marriage. He also points out the vacuity of the phrase, marriage equality, and he does this by recalling the Aristotelian concept of equality, which is that equality, rightly understood, simply requires that we treat like cases alike. It simply begs the question if there is no argument provided to the effect that same-sex relationships, polyamorous relationships, or incestuous relationships are alike in the relevant sense to natural marriage. Beyond this, he reminds us that marriage as a natural institution is removed from the rule of private, as well as public, will, when quoting the preeminent Scottish jurist, Viscount Stair in Institutions of the Laws of Scotland (1861):
Obligations arising from voluntary engagement take their rule and substance from the will of man and may be framed and composed at his pleasure . . . but so cannot marriage, wherein it is not in the power of the parties, though of common consent to alter any substantial . . . marriage arises from the law of nature and it is given as the very example of the Natural law.