Mind Matters Natural and Artificial Intelligence News and Analysis
Human fetus on scientific background
Photo licensed via Adobe Stock

Must We Be Able To Reason To Be Thought Of As Human Persons?

A common argument as to why abortion is generally ethical is that the unborn child cannot reason

Perhaps the most common justification that abortion proponents give for supporting abortion is that the human embryo or fetus isn’t capable of rational thought — and rational thought is the defining characteristic of humanity.

They’re wrong in a fundamental way. How they’re wrong is best understood if we look at the metaphysics of human development. Metaphysics is “The branch of philosophy that examines the nature of reality, including the relationship between mind and matter, substance and attribute, fact and value.” (American Heritage Dictionary)

The ancient philosopher Aristotle (384–322 BC), who provided an important foundation for science, pointed out that humans are rational animals. That is, we have at least the possibility of rational thought, although at some stages of life (e.g., in the womb) we don’t think rationally. Even as adults, we don’t think rationally all of the time.

Biologist and abortion supporter Jerry Coyne denies that zygotes (first stage of human development) have rational souls, or souls of any sort, when he writes,

And there’s no evidence [a zygote] has a soul or anything differentiating it from the embryos of any number of vertebrate species

Zygotes do have souls, in a quite obvious and non-mystical way. To have a soul (in Thomistic metaphysics, based in part on Aristotle) is merely to have the set of basic abilities and possibilities characteristic of life — the ability to metabolize, excrete, grow, the possibility to think and reason, etc. A soul is just a set of abilities and possibilities.

All living things have souls, because “soul” is defined as the characteristics that make them alive. The specific array of abilities and possibilities a living thing has determines what species of living thing it is. A tree has different abilities and possibilities than a man has. So Coyne is wrong to say “there’s no evidence [a zygote] has a soul”. If it’s alive, it has a soul.


Where, I ask, is the evidence (beyond that asserted by religious authorities) that abortion is identical to murder, even in its very early stages? There is clearly a developmental continuum in a fetus, with an abrupt break when the baby is born, and so drawing a line for when a fetus becomes equivalent to a person with rights, including freedom from “murder”, is purely arbitrary. Many Catholics, though, draw the line at a rationally insupportable stage: fertilization. A “person” is not created at fertilization: we have a zygote that now will go on to continue development. That zygote is an undifferentiated ball of cells without mentation or the ability to feel pain.

Coyne asserts that a zygote is not a person because it cannot think or feel pain. Of course, “person” is a moral and legal term — if it can be killed at will, without legal or moral consequence, then of course it’s not a person.

But does the lack of capacities — e.g., to think or feel pain — mean that a zygote is not a human being in the metaphysical (and scientific) sense? Living things with souls (like zygotes) are composites of two principles — potency and act. Potency is the possibilities that a living thing can have. An acorn has the potency to become an oak tree, if all goes well. Act is what the living thing actually is. An acorn is in potency to become an oak tree, and in act for being a seed.

A human zygote is in potency for the ability to think. A neonate can think, although in a rudimentary way. An adult can think in a more actual way, and an Einstein can think in a profound way.

At each stage of human life, the human being is a composite of potency and act. Each human being has things she might be and things she now is. This combination of “might be and is” — of potency and act — is what it is to be human. In that sense, the zygote is no different than the genius — they are both composites of human possibilities and human actualities. Every human being is a composite, you might say, of aspiration and achievement.

This composite of possibilities and realities is the essence of what it is to be human. A zygote is mostly potency, and little act. An embryo has more act and fewer potencies (because some have already been actualized). A child has more potency and less actuality than an adult, in the sense that the child can potentially do more things in the future and the adult can do more things now.

As we get older, actualities are realized and potentialities fall away. Human development is the dynamic realization of possibilities.

So of course Coyne is correct to say that a zygote can’t think or feel pain, but that does not mean that the zygote isn’t fully human. To be fully human at day one of gestation is precisely to have the potentiality to think and feel pain, but not the actuality (yet).

It would be quite odd if a zygote did calculus or said “ouch!” That is not what human beings do, a day after fertilization.

But human life is a continuum precisely because every stage of human life — from zygote to senescence — is human. A zygote is just as much a human being as you and I are. You and I were just as much human beings when we were zygotes as we are now, and we will be just as much human beings when we are on our deathbeds as we are now.

Children in the womb at every stage are certainly human beings, just as we all are. Human life is a developmental process of actualization of potencies. We grow, physically, mentally, and spiritually. No one is less than human just because of age or stage of development or ratios of potency to actuality.

We are all human beings at every stage of life. Whether we are “persons” or not depends on the reigning moral and legal definition of “persons.” The moral quandary — the agonizing and contentious moral quandary in the abortion debate — is not whether zygotes or embryos or fetuses or newborns are human beings (they are), but whether they are persons worthy of respect and protection.

The abortion debate is really just the tip of this question, the tip of this moral spear: are all human beings — regardless of ability — persons, with the right to life?

You may also wish to read: Do babies really feel pain before they are self-aware? Michael Egnor discusses the fact that the thalamus, deep in the brain, creates pain. The cortex moderates it. Thus, juveniles may suffer more. Jonathan Wells recalls, from when he was a lab technologist, how very premature infants would scream when he took a drop of blood for tests.

Michael Egnor

Professor of Neurosurgery and Pediatrics, State University of New York, Stony Brook
Michael R. Egnor, MD, is a Professor of Neurosurgery and Pediatrics at State University of New York, Stony Brook, has served as the Director of Pediatric Neurosurgery, and is an award-winning brain surgeon. He was named one of New York’s best doctors by the New York Magazine in 2005. He received his medical education at Columbia University College of Physicians and Surgeons and completed his residency at Jackson Memorial Hospital. His research on hydrocephalus has been published in journals including Journal of Neurosurgery, Pediatrics, and Cerebrospinal Fluid Research. He is on the Scientific Advisory Board of the Hydrocephalus Association in the United States and has lectured extensively throughout the United States and Europe.

Must We Be Able To Reason To Be Thought Of As Human Persons?