(22) Consequently, it seems necessary to stress the gravity and the irreplaceable character of some anthropological principles regarding the man-woman relationship, which are fundamental for human cohabitation, and all the more so for safeguarding the dignity of all persons.  The central nucleus and the essential element of these principles is the conjugal love between two persons who have equal dignity but are different and complementary in their sexuality.  It is the essence of marriage, as a natural and human reality, which is at stake, and it is the good of all society that is up for discussion.  “As everyone knows, not only are the properties and ends of marriage called into question today, but even the value and the very usefulness of the institution. While avoiding undue generalizations, we cannot ignore, in this regard, the growing phenomenon of mere de facto unions (cf. Familiaris Consortio, 81), and the unrelenting public opinion campaigns to gain the dignity of marriage even for unions between persons of the same sex”.[35][35]

This is a basic principle: in order to be real and free conjugal love, love must be transformed into one that is due in justice through the free act of marital consent. The Pope concluded in this way: “In the light of these principles, we can identify and understand the essential difference between a mere de facto union –even though it claims to be based on love—and marriage, in which love is expressed in a commitment that is not only moral but rigorously juridical.  The bond reciprocally assumed has a reinforcing effect in turn on the love from which it is derived, fostering its permanence to the advantage of the partners, the children and society itself”.[36][36]

Marriage, in fact, the foundation of the family, is not a “way of living sexuality as a couple”.  If it were only this, it would be just one of many possible ways.[37][37]  Nor is it simply the expression of a sentimental love between two persons: this characteristic is usually present in every loving friendship.  Marriage is more than that: it is a union between a man and a woman, precisely as such, and in the totality of their male and female essence.  This union can only be established through an act of the partners’ free will, but its specific content is determined by the structure of the human being, the woman and the man: mutual self-giving and the transmission of life.  Such self-giving, in the whole complementary dimension of a woman and a man, together with the willingness to owe oneself in justice to the other, is called conjugality, and the partners in this way become spouses: “This conjugal communion sinks its roots in the natural complementarity that exists between man and woman, and is nurtured through the personal willingness of the spouses to share their entire life-project, what they have and what they are: for this reason such communion is the fruit and the sign of a profoundly human need”.[38][38]