Abraham Lincoln once asked how many legs a dog has if we call a tail a leg. The answer, he said, is four: calling a tail a leg does not make it so. We chuckle and move on.

But what if people began to argue that a tail really is a leg? They might say that what defines the leg is that it is an appendage of the dog’s body, that it contains bone and muscle covered with skin and fur—just like a tail. Tails just happen to come out of the body at a different angle than other legs. When a tail hangs down low, who can tell the difference?

This is an example of defining a thing according to non-essential characteristics. It is like saying that a soldier is “a man who wears a uniform and carries a gun,” or calling a football stadium “a field surrounded by lots of seats.” It may be true in each case, but fails to tell the story.

To continue the figure, the bones and muscle of a leg are different from the tail. They have to support the dog and make it possible to run and jump. No matter how well the dog can wag its tail, it will not propel it anywhere. The issue, then, is not that the leg has bones and muscles, but how they are put together, and why. A tail is not a leg, because it is impossible for it to function as one.

Some may respond that there are legs on many dogs that cannot propel the dog anywhere. They have broken bones, or withered muscle, or have lost the foot in an accident. If not all legs can propel the animal forward, then this ability is not an essential characteristic of a leg. If lame legs are legs, so is a tail.

But a wounded leg is still a leg. Repair it, and it will function as one. If it cannot be repaired, this fact does not change the kind of thing it is. It is a leg, though damaged. The tail remains a tail.

The call for same-sex marriage involves a similar misdefinition. Marriage is often characterized today as follows: 1) two people 2) who love each other 3) want to perform sexual acts together, so 4) they consent to combine their lives sexually, materially, economically 5) with the endorsement of the community. Since same-sex couples can meet the first four criteria, how can society refuse the fifth?

It is easy to see why this would be a cause of aggravation, not only for same-sex couples who wish community endorsement of their relationships, but for millions of others. If the criteria stated above actually define marriage—and in contemporary Western society, many have come to view marriage as no more than this—then refusal to acknowledge and endorse same-sex relationships is a rank injustice, nothing but an exercise in bigotry or stupidity.

Typically, marriage does in fact have these characteristics. But why does marriage have these characteristics? Remembering why will help us to remember how they show themselves in a relationship that has the essence of marriage—and how that is often different in other relationships.

First, human beings have a powerful hankering to engage in sexual intercourse.

Second, sexual intercourse between a man and a woman naturally and frequently leads to children. Male and female alone each have part of a complete reproductive system. Without both parts, reproduction cannot happen. Without the result of children, it would be a real puzzler why we have these organ systems at all, and why we have such a deep urge to engage in sexual acts.

Third, the rearing of children is a lifetime responsibility. As deeply social beings, we remain connected to each other across generations. Even adults with children of their own need the wisdom and guidance of their fathers and mothers. It is easier for those who enter this project that they have affection for each other, and that they form a self-giving friendship. To perform these actions lovingly is the properly human way.

Fourth, because it leads to children, sexual intercourse has extraordinary public consequences. It is not, as we might like to think, a purely private act. It matters a lot to the community who is doing it, and under what circumstances. So the community endorses certain sexual arrangements; others, which fail to abide by the fullness of truth of human sexuality, the community rejects as unfitting for human beings. To support those that are fitting, it offers the institution of marriage. In marriage, the couple promises before the community to fulfill this project through vows of fidelity and permanence, joining their bodies and their lives to make the project work. The community promises to give the couple the privacy to perform their sexual acts, and care for each other; it further supports the family by means of appropriate protections and benefits. It may be that others could receive similar benefits for different reasons, but this is why benefits accrue to marriage: to help the marriage project flourish.

If sexuality did not naturally bring us offspring, it is hard to explain why it exists, whether you believe in a purely material evolution or a loving designer of the universe, for it would serve no purpose. If sexual acts did not naturally lead to offspring, it is just as hard to explain how marriage would have appeared in human history, for it would serve no purpose.

Religions may bless marriage, but they did not invent it. Because it involves such profoundly important human realities, it is no surprise that sex and marriage have religious significance. But sex and marriage have existed as long as there have been human communities.

If we accept the misdefinition of marriage using non-essential characteristics as the complete story, it would be impossible to reject same-sex marriage. Given the whole truth, however, it is impossible to accept it. No matter how superficially similar they are to real marriages, same-sex relationships cannot function as marriages.

Today, marriages crumble, families are torn, society flounders. Why? We are not living in the truth. We accept a bad definition of marriage, acquiesce to almost any sexual arrangement, glorify the quest for sexual pleasure, treat children as a means to fulfill our desires. Overwhelmingly, research shows that rearing children in any other environment than with both their natural parents is damaging. Sometimes that damage is unavoidable, as when a parent dies, but we shouldn’t seek it. And it certainly won’t help to say the impossible is real.

We need the truth. We need to fix the legs. Calling a tail a leg only makes matters worse.


Stephen J. Heaney is Associate Professor of Philosophy at the University of Saint Thomas in Saint Paul, MN.

Copyright 2010 the Witherspoon Institute. All rights reserved.