[ Term-mapping ]
Free - Consensual
Total - Public
Faithful - Exclusive
Fruitful - Sexual
I define “monogamy” as the public, exclusive, sexual, consensual relationship between two and only two persons. Because of the requirement of consent, the parties must be adults as defined by their culture.
(Further, the order of the modifiers indicates centrality:
Consent places violent relationships beyond consideration and means the soul/mind is involved;
Sexuality means the body is involved, and in a way different from other bodily acts;
Exclusivity means there is no artificial addition of other parties beyond the pair required for the act previously specified;
Publicity means the revealing of the relationship to others, beyond itself.)
There are two aspects to monogamy as defined above which make it ideal and normative.
The first is its satisfaction of human biology.
The second is its satisfaction of the human psychological desire for love.
These two are interrelated, as the human person is composed of both soul and body.
There is a state of actuality toward which each thing inclines according to its nature, causing it to act in a particular, patterned way. Material objects as material objects incline toward proximity (this force being called gravity). Living things incline toward their perfected form (as a seed grows into a tree, a young lion grows into an adult lion, etc). Parts of substances also act in a similar way, with the actuality toward which they are inclined being subservient to the actuality of the substance as a whole. Hearts pump blood, lungs facilitate gas exchange, leaves allow for opportunity to photosynthesize, etc. Similarly, the reproductive system has an actuality toward which it inclines--the production of new organisms of the same kind as the producer(s). In animals, this requires a pair of producers which have differing organs. It is the only organ system in animal physiology which requires more than one organism--specifically, two--of its kind to become actualized; the two act as one unit. (Some animals are capable of acting as both producers, but this is irrelevant to humans, which cannot.)
Further, the actuality produced is a fully human being, not yet in perfected state. This new human is incapable of bringing itself to the perfected state (adulthood), and requires many years of care. They thus require some person or persons to care for them, and if human life has a value in general, a “right to life”, such that their particular life does, as well, then someone must have a corresponding duty to preserve their life to match. It seems that this would naturally fall to the cause of coming into being; their two parents, mother and father. Since this is so, the two must remain together to accomplish the task they began, and therefore they must be able to cooperate and should receive the external support from the community to make this possible more easily.
So biology is satisfied by a unique pair of man and woman who work together to raise a child.
But by itself, this does not rule out polygamy, since one could have several such relationships simultaneously, though this would become more difficult owing to the finite time and resources available to a person. Yet even in that case, the “polygamy” is composed of a set of one-plus-one relationships.
Directly related to this is the problem of inheritance and property rights among polygamous cultures, due to the complexity of family systems. Historically, this has been a source of conflict.
Love has been defined as the “manifested will for the good of some Other”. So more than mere well-wishing, it includes the actual expenditure of time and energy to promote the good of the other person. So we see that love is a giving of self (and one’s goods) for the other. But while there are degrees of self-giving, the sort of relationship we are talking about is the most complete, and includes one’s body, and thus, one’s sexuality, and thus, one’s potentiality toward reproduction when paired with the complementary organs. (To ask a person to impede their fertility is to ask the person to modify themselves in order to become an object of love, which is instead to love the concept of that person after the modification, rather than as they are.)
In addition to each person in a couple giving themselves to the other, the couple, because of their unity, naturally seeks some Other to together give themselves to, to benefit that other person. In a two-person, heterosexual couple, there is a natural tendency toward the production of a new person, the child, toward which they are then able to direct their love. Other such relationships do not have this inherent tendency to bring about that Other.
So this degree or type of love is satisfied by a paired relationship of opposite-sex persons.
Beyond the utilitarian bond between the two because of the child, there is then also the prior bond between the couple as such, which, in a healthy relationship, seems to be desired as an unending relationship.
Special Focus on Exclusivity:
(It is assumed that we are talking about public, sexual, consensual relationships, so I will address the point of contention directly.)
The above shows that a [male-female pair] [N] is both necessary (it takes two to have sex or to have love from self to other) and sufficient (no third person is needed for sex, love requires only self and Other, and even the quasi third person as an object for love from the two-person quasi unit is accounted for by nature of a male-female coupling’s potentiality toward life) for a [proper sexual relationship] [S]. When something is both necessary and sufficient, then we can modify the phrasing to become [if S, then N:] “if there is a proper sexual relationship, then it is a male-female pair”. Thus anything in excess is not proper. QED.
But to add to that, we can see that in a loving, sexual relationship, the lives of the two persons are more interrelated than in mere friendships. (While contraception makes the difference less, it is still not entirely the same, and I would argue that the above serves to give merit to the case against contraception.) Because there is a greater union, there is a greater injury upon disunion, should that take place. So preventive restrictions must be imposed to reduce the risk of disunion--one such restriction being exclusivity. Further, should a child be produced, as is the natural tendency of sex, the child has a right to the care of their parents, and the parents have a right (and duty) to care for their child. This is severely complicated when familial relationships are broken. Historically, it is very rare that polygamy can be sustained without a loss of justice. However, there are more serious failures in sexual relationships, such as rape.
A public, exclusive, sexual, consensual relationship which is acknowledged by the state or community at large in a formal manner is what is known as “marriage”. As the above makes clear, this is also ideally a permanent relationship. So we find the “traditional” view of marriage and sexuality to match the biological and amorous aspects of the human person.