Theirs is not a “definitional” argument. They do, indeed, argue that marriage is a distinct “object in nature,” (they refer to it as a ‘human good’) a reality which, by any name, would be recognizable to any rational being.
Before I set down my rather inept summary of the argument in the book, a disclaimer is in order. The extent to which the authors support and augment their thesis is very important to truly grasp how cogent their statement of the argument really is.
The central argument is that there exists in the nature of humanity and reality itself an undeniable “good” for human beings. That “good” is a uniquely integral state or manner of human existence commonly called “marriage” which can only be realized by a heterosexual pair of human beings. This “state” is conjugal in essence and differs from other relationships such as friendships, sibling relationships, parent-child relationships, golf-buddies, sports teams, and, in short, any other kind of relationships that human beings can become a part of.
Conjugal marriages are unique in that these involve the “coming together” of two distinct but compatible human persons along physical, psychological, spiritual and social “planes” for an intended end - to further the physical, psychological, spiritual and social relationship of the conjugal pair in space and time. The pair becomes “expansive” in its relationship by its unique ability to create new embodiments of their relationship in real space and time. No other human relationship can do this, which is why conjugal marriage is unique and one of the reasons why it ought to be treated uniquely under the law.
The authors deal with all the standard objections to the “conjugal” view of marriage and reply effectively to the typical “revisionist” arguments. This book should be required reading for anyone seeking to understand what a redefinition of marriage entails and why it will ultimately fail - at least in any society that seeks its own survival and continuance.
