In my last piece, I introduced a philosophy of human nature called personalism. I said personalism referred to any anthropology or morality that looks to personhood as the outstanding attribute of human beings, the attribute which invests them with special value, sometimes called human dignity, and elevates them in value over all non-personal beings, indeed over all material creation, and because of which, humans are said to possess rights and immunities.
In this piece I look at personhood itself. I ask what it means when we say human beings are persons. I draw on philosophical insights from Aristotle, from Christian philosophy especially St. Paul, St. Augustine (354-430AD) and St. Thomas Aquinas (1225-1274AD), and from the mid-twentieth-century French-German school of thought called “Ressourcement” (or “Nouvelle Théologie”), the most influential proponent of which is the great German theologian and pope emeritus, Joseph Ratzinger (Pope Benedict XVI).
I present here only a philosophical description. The Christian tradition also, of course, includes prominent theological truths about human nature. I hope to take these up in a future piece.
Five Essential Qualities
Human nature has five essential elements; each element is necessary to an adequate description of the human person, and none is more essential to human nature than another.
The human person is …
(1) Substantially One. This means persons are whole, living beings with a material body and a non-material soul. Although they have many capacities (e.g., rationality, emotionality, creativity), the activity of any capacity is always and necessarily the activity of the whole person. It is not John’s mind that thinks, but rather John.
(2) Bodily. Properly speaking, I don’t have a body, I am a body, although not only a body. This implies two things: all human persons are bodily; and, following from number (1), every living human body is a person. Our bodies are not our possessions upon which we express our creativity, as an artist possesses a canvas upon which she expresses her skill. Nor are they grand machines that we operate, like a captain operates a ship.
What’s at stake here? Literally life and death. Behind the reasoning of many defenders of abortion and euthanasia is a faulty conception of the body. For example, if I am not always my body, but rather some ghostly reality (call it mind) inside of an organic machine, or if I didn’t become a person until the body that later became me acquired some ability (say, consciousness), then when there is no indication that the mind or the consciousness is present (say I am suffering in what appears to be an irreversible coma, or I am at the embryonic stage of development), a living body would exist, but no person. Terminating this body’s life then would not be killing me; not be homicide. You can see how this faulty reasoning might become the philosophy-du-jour for the right-to-die movement as well as those defending embryo-destructive research.
Bodiliness also implies biological gender. Human bodies are not generic; they are male and female. Each body has a distinct sex, the vast majority of which are easily identifiable by looking at primary and secondary sex characteristic and genetics. If bodies are personal, and bodies exist as male or female, then not just the consciousness or emotionality of a person are engendered, but the whole person is either male or female. (I have addressed the question of intersex  children elsewhere.)
(3) Interpersonally Relational. Persons are naturally social and hence have natural inclinations and needs for life in society. There is much more that could be said here, but for economy’s sake, we’ll save it for another essay.
(4) Rational. Not every person is capable of exercising rationality (e.g., the unborn who need more development, or the comatose who suffer from pathology that blocks its expression). But every person is a rational being; each possesses a rational nature, either yet to be fully realized, functional, or having the potentiality, however remote, to be healed.
As rational, persons are able to know others and themselves; know truth and the world around them; know good and bad, and that good is to be done and pursued and bad avoided. They can know the precepts of the natural  law  that guide human action in accordance with human flourishing. And they can appreciate what is beautiful.
(5) Volitional & Free. Finally, persons have free-will. This makes them capable of responsibility for among other things the kinds of people they become. If they become courageous, honest and temperate, or feckless, crooked and lecherous, it is their own doing, perhaps not entirely, but always also their own. It also makes them creative; they can bring into existence things that once did not exist. And it makes them capable of giving and receiving love.
So what makes humans special, different from and superior to every other creature in the universe? Humans are special because they are persons. They are persons precisely in virtue of the distinct natures they possess, a nature constituted of a material body and a non-material rational soul. They become persons the moment they come into existence; after a few dozen months of development, and, if unhindered by pathology, they become capable of expressing capacities they’ve possessed in seed form from the beginning: responsibility, creativity, and most importantly, love.