A Rational Nature Confers a Right to Life

Around 1980 I would have said, and probably did say, that although abortion is a repulsive procedure, it is morally permissible, and therefore should be legally permissible. In the three decades since then, I’ve come to a very different conclusion. Here is my reasoning, in outline. I am happy that my reasoning has been guided by the moral teaching of the Catholic Church, of which I am a member, but it does not rest in any way on the Bible, revelation, or infallible authority—it rests, as any moral reasoning should, on pure reason.

I expect some people will find some holes in my argument. Please be so good as to point them out; this exposition will be very terse, and it is a work in progress.

1. Modern science does indeed show us that a new human life begins to be at conception: when a human egg and sperm unite, a new individual life form of the species Homo sapiens begins to exist, with its own unique DNA.

However (as, unfortunately, many pro-life people fail to recognize) we cannot leap directly from this scientific result to the moral conclusion that the newly conceived human has a right to life. Science is value-free. It tells us nothing about whether this human life, or any human life, has rights. That is a philosophical question. And some philosophers have (unfortunately) questioned whether every human being has a right to life, because they think that some human beings are not persons. So we must examine what it is to be a person, and why is it that human beings are persons and have a right to life.

2. Human beings have rights, including a right to life, by virtue of being persons: individual substances of a rational nature (Boethius’s definition of “person”). By “substance” I mean an individual being or thing, such as a stone, a tree, a horse, a man. By “rational” I mean having the power of reason. Reason includes, among other things, the ability to recognize and be guided by the moral law. A rational being is capable of discerning right from wrong, choosing good and avoiding evil. By “nature” I mean the intrinsic or essential properties of a being—as the etymology of the word would suggest, what the being is born with—although the nature predates the time of birth.

If ever I should meet an “intelligent” being of another species, perhaps an alien from another world, this is the criterion I would think appropriate for deciding whether it has full moral rights, what we call “human rights”: is that being capable of morality?  The capacity to feel pain endows a being with animal rights, but not human rights (or else let’s all become vegetarians). The capacity to calculate or make formal logical deductions (as in some forms of artificial intelligence, either now or in the future) is simply not morally relevant. But the capacity to act as a moral agent seems to be necessary and sufficient. If an agent is treating me morally, I should treat it likewise. If it does not and cannot, it would seem unfair for me to be obligated to recognize its rights, when it does not and cannot recognize mine. So a rational nature—which is a nature capable of supporting moral thought and action—is one that entitles the being possessing it to full human rights. It is because we are rational in this broad sense—which is what people mean, or at least part of what they mean, when they say in religious terms that man is made in the image of God—it is because we are rational beings that we have human rights.

3. The life form that begins to be, when a human egg and sperm unite, is an individual substance of a rational nature, though not yet actually rational.

The unborn human has a rational nature, but that rationality is not yet realized: it is not yet actual.

A person sleeping also is not being actually rational, but that person has a right to life.

Fine, you may say, but before going to sleep, the person was actually rational, and that actual rationality confers a right to life which persists even during sleep.

But children, also, are not actually rational, and have not yet been actually rational; and still they have a right to life. Children have a rational nature: if they develop as they should, they become rational. They become morally capable and morally responsible at a time traditionally called the “age of reason,” around seven years of age. But before that, they already have human rights. They have these rights, not because they are actually rational, or have ever actually been rational, but because of their rational nature.

4. Therefore, the unborn human being also has human rights, including a right to life.

5. The United States Supreme Court ruled, in Roe v. Wade, that a pregnant woman has a right to an abortion because of her right of privacy. Of course, everyone has a right to reasonable privacy in the natural law. Whether or not the U.S. Constitution guarantees a right to privacy of this kind is something that I will not discuss. Regardless of that, the right of privacy is not absolute. In particular, the right of privacy does not trump the right of life. Otherwise I would have a right to shoot people to prevent them from seeing me naked.


Original version, October 4, 2015.

Revised January 20, 2019, to clarify why the question of personhood is important, to connect the rationality of human persons with the idea of “made in the image of God,” and to clarify privacy rights are relevant.

Revised July 11–12, 2025, to clarify “substance” and to make the age of reason = 7 instead of 12 to 14, although Rousseau thinks that reason is not attained even at the age of 15.