An Aristotelian Defense of the Pro-Life Position

Ancient Greek philosophy, which undergirds our western way of thinking, can provide insights into the current debate over the morality of abortion. There is a false idea prevalent in our culture today that science is the final arbiter of human knowledge (1). Science, alone, cannot reveal knowledge to us, however. Science can only study and give us knowledge about the physical aspects of reality. It has nothing to say about the metaphysical aspects of reality, or about whether there is a metaphysical reality or not (2). Science is merely a tool to gain knowledge and insight into physical reality. In order to properly engage in a scientific endeavor, one must already have a worldview for interpreting scientific findings. Philosophy provides such worldviews. Philosophy has also given us logic—principles for reasoning—which science must assume and cannot prove. Philosophy is more fundamental than science, which is why science is also known as “natural philosophy.”

In philosophy, there are a number of so-called “problems” that are relevant to the abortion debate, such as the “mind-body problem.” However, as philosopher Edward Feser explains, these problems did not crop up until Aristotelian essentialism started to be rejected by philosophers (3). As Feser writes, rejection of essentialism was the “single greatest mistake ever made in the history of modern thought (4)." In fact, he tells us, without making the distinctions that essentialism makes, you can’t even fully understand the abortion debate (5).

This essay will use Aristotelian essentialism to present a proof for the truth of the pro-life position (6). It’s important to point out that Aristotle was not pro-life in the modern sense of the term. The ancient Greeks had different ideas about the value of human life than Christians do, and they practiced abortion and infanticide before the influence of Christianity ultimately ended the practice of infanticide in ancient western countries (7). But it’s undeniable that Aristotle’s metaphysics shows that human beings are human right from the start.

What is Essence?

The first step in our argument is to talk about essence. What is essence, and how do you determine the essence of a thing? A thing’s essence is essentially what makes that thing what it is, what differentiates it from something else. If we consider the abstract concept of triangularity, what is its essence? The essence of triangularity is that it has three sides and three corners that add up to 180 degrees.

Triangularity is a “universal,” meaning that there can be numerous instances of this abstract object; universals can be had by more than one individual thing at a time (8). An individual triangle is a particular instance of the universal abstraction triangularity. Such a particular instance of a universal is referred to as a “particular.” In the same way, the abstraction “redness” is a universal (there can be many red things), but a red apple is an individual instance, a particular, of redness.

Once we have determined a thing’s essence, we can then determine what properties are essential to the thing which makes the thing what it is and not something else. Since we know that triangularity means having three sides and three angles, three sides and three angles are essential to an entity being a triangle. If I draw a polygon with four sides, it is not a triangle but a rectangle that I have drawn. Since three sides and angles are what makes a triangle a triangle and not something else, if I draw a figure with four sides and four corners, it cannot be a triangle. An essential property is any property of an entity that if the entity were to lose that property, it would cease to be what it is.

In contrast to needing three sides and three corners, what color the triangle is and what material it is drawn on are accidental to triangles. If I draw a red triangle on paper and a blue triangle on a chalkboard, both are particular instances of triangularity, despite being two different colors and being drawn on two different material surfaces. An accidental property is any property of an entity that does not affect what the entity is. Having or not having a particular color does not affect what a triangle is.

Having clarified what essence and essential properties are, we can now determine what makes humans what they are and what differentiates them from non-humans. In other words, what is the essence of humanity?

Humans are a specific kind of animal, the kind of animal that can engage in rational thought. The capacity for rational thought is what separates us from other animals, as well as other living things, such as plants and trees. Since what sets us apart from lower animals is our capacity for rationality, one can say that humans are rational animals. To be capable of rational thought is inherent in being a member of the human species. This capacity for rational thought is an essential property of humanity, and other things, such as eye color, skin color, or being conscious, are accidental properties. As long as an entity has this capacity for rational thought, that entity is a human being (9).

The prenatal entity produced by a human woman and man is identifiable as biologically human once it comes into existence during the fertilization process. In other words, the unborn are biologically human from the beginning, which means that they have the inherent capacity for rational thought, which flows from the individual’s rational nature.

To repeat, to be human is to have the essential property of having a rational nature, from which flows the inherent capacity for rational thought. It is this inherent capacity, not whether or not it is presently exercisable, that is necessary to ground one’s identity as a human being. Being human does not depend on accidental properties such as higher thought, speech, movement, or the like.

Claiming that you are not a person until you possess certain accidental properties is to confuse what you are with what you can do. All members of the human species have rational natures regardless of the kinds of things they can do. Given Aristotelian essentialism, it is certain that the unborn are full human beings from fertilization.


1.) This religious devotion to science by atheists has been called scientism by Christian thinkers.

2.) The term “metaphysical” simply means “beyond the physical.” It refers to those aspects of reality which are not immediately accessible to the five senses, and usually require philosophical reflection in order to find truth in this area.

3.) Edward Feser, The Last Superstition: A Refutation of the New Atheism (South Bend, IN: St. Augustine’s Press, 2008), 51.

4.) Ibid.

5.) Ibid., 57.

6.) Entire books have been written in defense and explanation of Aristotelian Essentialism. This will only be a very basic treatment of these ideas. Essentially (no pun intended), I will only be talking about the portions relevant to the argument.

7.) This is why certain philosophers, such as Peter Singer, argue that we should have legalized infanticide (on top of legalized abortion), to get away from “antiquated” views of human value.

8.) On the surface, it seems strange to refer to a concept as an “object.” However, Plato and Aristotle believed (as do modern Aristotelian philosophers like Feser and David Oderberg) that abstract things such as triangularity, justice, morality, and so on, are real objects that exist in reality. Plato believed these abstract entities (which he called “forms”) exist in some third realm beyond the physical and mental, the realm of forms. Aristotle believed that these forms did not exist in some third realm, but instead exist, in some sense, in the mind (which is perceived by human beings) and in some sense, in the thing itself.

9.) Here is where a clarification is essential. All human beings have the capacity for rational thought. There are certain extreme cases, such as anencephaly, which are appealed to in order to try and argue that not all humans have the capacity for rational thought. It is beyond the scope of this essay to go into detail regarding the different kinds of capacities, but suffice it to say that children conceived with anencephaly, or some other severe disability or defect, still have the inherent capacity for rationality by virtue of their human nature. This capacity is just tragically blocked by an external factor (injury or disease). It is not possible today to restore a severely disabled child’s capacity for rational thought so the child can actually exercise it, but it may be possible someday. Here’s an example to illustrate this further: 100 years ago someone with severe damage to their corneas was blind and could never see again. As a human being is, by nature, an entity who can see, this inherent capacity was not lost, but the presently exercisable capacity became blocked by an injury to the cornea. Today it is possible to give a cornea transplant to certain people who have gone blind, even though it wasn’t possible 100 years ago. It would be silly to assert that the inherent capacity was lost 100 years ago but not today, when cornea transplants are a reality. Even so, just because humans do not have a way to restore lost brain function, it does not mean the inherent capacity for higher brain function—including the capacity for rational thought—has been lost due to severe brain injury or disease.


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