What is a Person?

Debates about abortion, euthanasia, and the recent case of Alfie Evans all turn on the question of personhood.

We all agree murder is wrong, but what counts as murder? Most of us don’t think murder and killing are per se identical or morally equivalent. After all, if you eat meat, you most likely believe that taking life is not in principle wrong; and our current laws reflect this presumption.

Perhaps, you’d suggest, it’s not taking life that is in principle wrong, but taking specifically human life. Or perhaps taking innocent human life (since for most of human history, things like corporal punishment and just war have been relatively uncontroversial matters).

Modern ethical and political thought since the Enlightenment has developed a distinct way of talking about this issue: the language of “rights.” Government is founded for the sake of preserving rights; and the most fundamental right is usually agreed to be that of life.

Most Western legal systems operate on the assumption that rights are not predicated of humans qua humans, but humans qua persons. It is personhood, not humanity, that grants one rights, at least to many of our courts and governments.

So how we answer the question of what a person is, and what counts as a person, determines quite a bit.

Today, the notion of personhood is closely associated with concepts of individuality, intellect, will, emotions, desires, etc. For our sake, we can include all of these under the general label of “conscious mental activity.” On this view, a certain minimum level of conscious mental activity is a necessary prerequisite for attaining the status of personhood.

In all honesty, this view carries with it a certain initial plausibility. After all, when we speak of “persons” colloquially, something related to this notion is most often what we have in mind. Think, for instance, of common derivatives of the word person: personal, personality, personally, etc. Wherever you stand on the abortion question, it’s admittedly difficult to conceive of a fetus having a “personality.”

The problem is that our colloquial use of the word “person” does not accuratley reflect its historical meaning or significance. Traditionally, the word “person” has not been predicated of specific attributes, but rather of that which grounds those attributes. So Saint Thomas Aquinas defines a person as an “individual substance.” In particular, a person is an individual substance of a rational nature.

Human beings have rights/dignity/value/worth because human beings are rational creatures. Given this, what difference does it make if we define a person as an individual substance of a rational nature as opposed to an individual which possesses a certain minimum level of mental activity?

For one thing, the latter view is extremely problematic. How do we determine what that minimum level of mental activity is? There does not seem to be any non-arbitrary method of determination. Perhaps, one might say, if rationality is what gives humanity dignity, then the ability to utlize or realize rationality should be considered a minimum standard for personhood. But then we run into several problems: first, infants and young children don’t have developed rational abilities. Are we prepared to say that infants are not persons and have no right to life? And what about the fact that adult humans are not always in positions where they are actually using or realizing their rational potentials, e.g. such as while they sleep? Are we prepared to say that humans cease to be persons (and hence lose their right to life) while they are asleep? One could, of course, attempt to modify the principle such that it fits these various difficulties, but then it becomes difficult to see how the formation of the principle is not, as we’ve suggested, ad hoc or arbitrary.

The better approach is to say that human dignity is grounded in human nature; and human nature is possessed by any living human organism. An individual organism which possesses a specific nature is an individual substance within that nature, and hence is, in the relevant sense, a “person.” The implications, then, are that fetuses are both human beings and human persons, and as such have a “right to life,” meaning that killing them is wrong and thus that abortion is gravely immoral.



[1]. https://people.howstuffworks.com/personhood.htm

[2]. Aquinas. Summa Theologiae. I, Q. 29, Art. 1. http://dhspriory.org/thomas/summa/FP/FP029.html#FPQ29OUTP1


21 thoughts on “What is a Person?

  1. The philosophical question of what constitutes personhood still remains, and Aquinas’s definition of person is not every phiosopher’s. There are different philosophical and also legal definitions of personhood. Fact is, nobody is going to send you to prison for first degree mass murder even if you deliberately cut off the power to a refrigerator filled with frozen human zygotes. Property loss, yes.


    1. True, Aquinas’ is not every philosopher’s definition. But I’m suggesting here that it’s perhaps the best. And whether or not one *would* send me to prison for such an act, does not determine whether or not one *should* send me to prison, or whether or not the action itself is morally right or wrong.


      1. Mere attempts at deflection, not evidence, far from proofs, you might as well simply repeat, “I am right, I love Aquinas and Catholicism, they are the last words, and they must both be right (except of course for those times when Aquinas was wrong). Nor do you recognize any differences in how people react to single cells dying, including zygotes, if they are nonAquinians. Heck, Thomas himself surmised that the soul entered during the quickening, not earlier.

        And speaking of “souls,” there are Christian monist philosophers who don’t view souls as separate from bodies/brains. They point out that in the OT we ARE souls, instead of the later notion that we HAVE souls: https://etb-history-theology.blogspot.com/2012/04/mind-body-dualism-and-possibility-of.html


      2. Edward, I am not attempting to deflect anything. In the article above, I gave my reasons for thinking that other notions of personhood are problematic, whereas Aquinas’ definition of personhood helps solve some of the difficulties. If you would like to respond to those reasons, we could have a substantive dialogue. I’ll repeat a brief outline of my reasons: 1) If personhood is defined by a certain minimum level of mental activity, how do we determine that minimum level in a non-arbitrary fashion? 2) If personhood is defined by a minimum level of mental activity, does this not have the potential of excluding infants and even sleeping adults? Aquinas’ understanding of personhood satisfies both of these difficulties. And you’re right, I do love Aquinas, and I do love Catholicism. I am, after all, a committed Catholic and a student of Thomistic philosophy. As for the point about recognizing a difference in people’s reactions to zygotes dying to people dying, I certainly do recognize that there is a start difference in reactions. I just don’t think emotional reactions, on their own, constitute good arguments.


      3. You asked, 1) If personhood is defined by a certain minimum level of mental activity, how do we determine that minimum level in a non-arbitrary fashion? 2) If personhood is defined by a minimum level of mental activity, does this not have the potential of excluding infants and even sleeping adults?

        Reply: If there isn’t even an embryonic brain yet, or the brain waves are so immature as to resemble a preconscious state (Jello has EEG readings), then those are among the most minimal levels. Concerning sleeping adults, their brain waves during sleep are equal to those during wakefulness, a lot of electrical activity can be measured even while unconscious, and a sleeping adult has a whole history of interacting with many others and society at large in many sensible and intellectual ways, but a zygote or early embryo has none of that. As for infants, exiting the womb is when physical bonds are enlarged to a gargantuan extent with multiple family members and society at large, as well as when the newborn’s senses come into full contact with the outside world, family and society. Even in the fourth Gospel Jesus is depicted as speaking about being born again, stressing birth not conception as an overwhelmingly momentous occasion.


      4. Interesting points. But my question is about minimum level of *mental* activity, not *brain* activity. Mental activity consists of things like self-awareness, personality, desires, emotions, etc. Whether or not these are ultimately reducible to brain functions, we tend to think that it is the qualitative aspects which are in themselves valuable. So yes, a sleeping adult has a significant amount of brain activity, but *not* necessarily mental activity. If we’re going to say that in actuality it is the physical brain activity that is the possessor of value, then it seems we’d have to conclude that Chalmer’s philosophical zombies are *as* valuable as regular humans, which doesn’t seem true.


  2. What exactly is an “individual substance?” Beyond a mere phrase, what can you say for sure that it means? And how can you prove it? Is Aquinas’s view of “substances” equivalent to today’s usages?


  3. I was asking rhetorical questions based on philosophy of language. Calling something an “individual substance” is about as vague as one can get. One can prove anything to one’s self by employing such vague terms. Like Aristotle knew all about nature and substances and the grounds and properties of things.


    1. The term has a long history in philosophy, theology, and natural science. The first link I gave should give you a better feel for what Aquinas means when he talks about substance, and the second reference should offer some of the reasons we have for thinking Aquinas was right. Did Aristotle know everything? Of course not. Did he know a lot? Absolutely. He deserves to be taken very seriously


      1. If by science today you mean modern natural sciences, probably not very much (because modern science since Descartes was founded on the goal of eliminating substances from scientific description), but if by science you mean the pursuit of knowledge in general, then very much. One example: it helps solve the problems of change and identity over time


  4. A few thousand years ago “human nature” and “living human organism” had the same demarcation problem you identify for mental capacities. It is only because we killed off our fellow hominins and created a substantial gap between species that the distinction can be made.

    It also isn’t clear to me why we should think that a criteria is superior because it simplifies partitioning. If the partitions do not align with our values then they only serve to create conflict.

    Liked by 1 person

    1. Your point is well taken. One of the primary challenges posed to Aristotelians by evolutionary science has been the problem of identifying where different species become actually different substances. I think you’re right that two species closely related in genetic material would be extremely difficult to differentiate metaphysically. But, I don’t think that necessary undermines what I’m saying here. My claim is that human nature has dignity precisely because it has the power of rationality. Whereas many biological features are distinct only in terms of degree, rationality is a qualitatively different kind of feature; and as such I think demarcating rational creatures from lower species, even ones biologically quite similar, would not be impossible.


      1. What makes you say that rationality is not a matter of degree? At what point between embryo and adult does a human pass the threshold of being uniquely rational?


      2. Sorry to take so long to get back to you. I think rationality can come in degrees in the sense that rational agents can actualize their rational powers to differing extents, but I think the power of rationality itself is something qualitatively higher than mere biological features. For instance, the difference between a modern ape and one of its ancient ancestors is going to be a difference in biological features that differ in degree; whereas, I think, a modern human is qualitatively superior to a modern ape insofar as it has the power of rationality.


      3. Yes. Although we should differentiate between an active power and a passive power. Here’s what I mean: A man who has learned to speak Chinese, but is currently not speaking it, has the power to speak it. But so does a man who has never learned Chinese. The former is an active power and the latter is a passive power. I think we should say that a human embryo has a passive power of rationality


      4. Does a human embryo with a genetic mutation that will constrain their rational capacity to something less than a chimp still have this “passive power”?


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