The Substance Account for Equality

Human equality is an important value in our world today. We want equality between the races. We want equality between genders. We even want equality between humans and animals. 

But to have equality, we have to figure out what it is that makes humans equal. For myself, I believe human equality is best grounded in what Scott Klussendorf calls a substance view of persons:

Substances are living organisms that maintain their identities through time, while property things, such as cars and machinery, do not. What moves a puppy to maturity or a fetus to an adult is not an external collection of parts but an internal defining nature or essence. As a substance develops, it does not become more of its kind but matures according to its kind. It remains what it is from the moment it begins to exist. Consequently, a substance functions in light of what it is and maintains its identity even if its ultimate capacities are never realized due to disability or injury. A dog that never develops his capacity to bark is still a dog by nature.” (1)

I am a human substance. I remain a human substance throughout every stage of my development. In fact, it is my human nature which drives my development. And that human nature is the one trait that I share with all other human beings equally. Therefore, our nature is the best thing to ground human equality in.

When it comes to the abortion debate, the question of the equality of the unborn is the focus. The pro-choice side says that having a human nature is not enough.  

Often pro-choice advocates will argue that what makes a human worthy of equal rights is when he or she becomes a person. They have many different ideas of when that happens but a very common stage put forward, famously argued by Mary Anne Warren, is when the unborn achieves consciousness. Consciousness allows you to become sentient which in turn leads to the capacities for emotion, rationality, the ability to communicate, self-awareness, and moral agency. (2)

Klusendorf responds to this kind of argument by saying:

Human embryos have a basic (root) capacity for self consciousness, lacking only the immediate capacity to exercise it. As [Robert P.] George points out, human embryos possess this basic capacity in virtue of the kind of thing they are – members of a natural kind, a biological species whose members (if not prevented by some extrinsic cause) in due course develop the immediate capacity for such mental acts. We can therefore distinguish two types of capacities for mental functions: 1) immediate and 2) basic or natural.” (3)

What Klusendorf is getting at is that from the moment of conception onwards, humans have the basic capacities that give them the potential for self-consciousness and rational thought. The only thing that differentiates them from us is their level of development.

But this leads to two questions. First, as Trent Horn asks, in what other cases do we say level of development disqualifies humans from being a person? (4) Second, when does the level of development determine a human having a right to life? Horn gives the following hypothetical:

After all, infants cannot function like adults in the sense of being able to think rationally, but we don’t say they have the “sentience of a cow” (even though they have about the same level of brain development as a cow.) We don’t say a mother, by virtue of being older and more developed than her infant son, has the right to kill her infant son or that her rights “trump” his. Why shouldn’t we treat all human beings equally, regardless of how developed they are?” (5)

But are proponents of the substance view correct in thinking all humans share the same basic capacities? This article will focus on pro-choice philosopher David Boonin’s critique of the pro-life case for equality based on substance. 

David Boonin Critique

In his book, Boonin focuses on Stephen Schwarz’s argument from basic capacities in which he says the unborn is a being “the basic inherent capacity to function as a person, regardless of how developed the capacity is, or whether or not it is blocked, as in severe senility.” (6) Boonin offers several critiques of this argument. First, he explains his understanding of it: 

I take it that he means… that it is an essential property of every living member of the species homo sapiens that it has the capacity to function as a person. If this is so, and if the capacity to function as a person confers on one a right to life, then being a member of homo sapiens does ensure that one has a right to life.” (7)

Boonin sees two problems with Schwarz’s argument. 

The first is that the claim that every member of homo sapiens has the capacity to function as a person is false. There can, for example, be human fetuses with such severe deformities that they will never develop a brain capable of sustaining thought, or even a brain at all.” (8)

The second issue he raises is that:

The species essence argument rests at least in part on the claim that the fact that you now have the capacity to be able to do something later imposes moral limits on how we are permitted to treat you now. Even if we concede that every human being had this capacity… we still need a defense of the moral significance of the fact that the fetus now has the potential to do the sorts of things later that you and I can do now.” (9)

To properly respond to Boonin, we need to be able to answer two questions. First, do fetal deformities refute the pro-life contention that all humans have the basic capacity for self-consciousness and rationality? Second, does the pro-life position rest on what humans have the potential to do later in life?

If Only I Had A Brain

Boonin makes one critical mistake in his summary of Schwarz’s argument. This in turn affects how well the rest of his rebuttals work. Schwarz did not just say capacities, he said “basic capacities.” Boonin completely misses this. As a result, Boonin inadvertently sets up and knocks down a straw man. He responds as if Schwarz is saying all humans share immediate capacities equally. Boonin shows with his example of fetuses with deformities that this is not true. Not all humans have the immediate capacity to express rational, conscious thoughts. But proponents of the substance view like Schwarz have already granted this. (10) This does nothing to show that all humans have the basic capacities though.

Boonin does notice how Schwarz acknowledges that some fetuses have deformities which block them from developing immediate capacities. But he thinks this creates more problems for the pro-life side: 

“it is difficult to see why we should not also call the spider crawling up my window a person. If he were able to develop a big enough brain, he too would be able to function as a person, so he is simply a person whose capacity is blocked by the fact that he will never have a large enough brain.” (11)

In reality though, this would have only been a problem if Schwarz was basing personhood on immediate capacities.  The spider is its own substance with it’s own way of developing. It’s stages of development do not include ever growing a brain and becoming rational like us. Therefore, unlike the newborn baby, it is not blocked by a stage of development but by what it is. The deformed infant’s substance has not changed. It’s basic capacities remain the same. (12) Rather it’s blocked by an illness that stunts it’s stages of development. But if  we consider born humans who have been similarly stunted  persons, why can’t we also consider unborn humans with disabilities the same. 

I Just Don’t See A Future

Boonin asks  why the unborn’s potential to do something in the future imposes moral limits on what we can do to the unborn now. I interpret Boonin here as trying to grant the substance view for the sake of argument. This is really his way of asking what the argument proves.

A couple of points can be made here. First, since Boonin didn’t understand Schwarz’s argument to begin with, he’s not actually granting anything. He has turned the pro-life argument into another version of a pro-choice position where human rights are based on immediate capacities.

Second, the answer is that it’s not the unborn’s potential to do things in the future that imposes moral limits on us. It is what they are now: human beings. The only difference between the unborn and us is their level of development. And as I showed at the beginning, level of development is not something we normally base personhood or the right to life on. So we need a good reason to do it in the case of the unborn.  

Eventually, even pro-choicers have to fall back on grounding human life in what the newborn are, not in their level of development.

Boonin’s Changing Standard

Boonin himself eventually is forced to ground human rights in what a being is, not in what their abilities are. He believes that the unborn attain human rights once they develop cortical brain activity. This is where consciousness is present and where people can begin having desires, such as the desire not to be killed. (13) I imagine having a conversation with Boonin going something like this:

Me: David, even with cortical brain activity, the unborn and the newborn are probably not thinking, “Boy, I really wish no one would kill me right now.”

David: Well, no, Chris; they may not have the occurrent desire not to be killed. But they do have the dispositional desire.

Me: I’m not sure what that means.

David: Well, the occurrent desire is the one you have when you think “Boy, I don’t want to be killed right now.” The dispositional desire is the one you have, even when you are not thinking about it.

Me: So, maybe someone could be planning on killing me and I don’t know about it. But if I did know about it, I would desire that they not murder me.

Boonin: Precisely.

Me: Okay, but what about the suicidal teenager? He does not have a desire to live either. In fact, he might desire to die. So would it be wrong to kill him just because he desires to die?

Boonin: No, because here we have to distinguish between someone’s actual desires and their ideal desires.

Me: Okay. And what’s the difference there?

Boonin: An actual desire is the one you are currently experiencing. But the ideal desire is the desire the depressed person would have were circumstances not so bad. When there is a conflict between actual desires and ideal desires, we should respect the ideal desires. (14)

Here, Francis Beckwith gives a helpful hypothetical situation that ultimately shows that Boonin relies on what the human is to ground human rights.

Me: That leads to the problem of the indoctrinated slave.

Boonin: I have not heard of that.

Me: As Francis Beckwith explains, imagine that you own a slave. And you brainwash them so well that they actually do not desire things like freedom, or the right to life. The obvious question is, do they lack the right to life and freedom just because they’ve been programmed so it doesn’t matter to them?

Boonin: No. But that is where I would appeal to their ideal desires. (15)

Me: But then as Beckwith writes:

But that judgment seems to assume that the slave is a being of a certain sort that ought to desire a right to life even when he does not actually desire a right to life. Then, it is not desire that grounds the right to life, but the nature of the sort of being that would have this correct desire if it had not been indoctrinated, or will have this correct desire when it reaches a certain level of maturity and it is functioning properly.” (16)

And then we are right back to the question of why, if you can grant a born human the right to life based on what they are, you can’t do the same for the unborn?

Ironically, as my friend Paul Chamberlain pointed out to me after reading this article, Boonin may have actually handed us a new pro-life argument. The unborn have dispositional and ideal desires too, by his logic. Therefore, it would be wrong to kill them. Thanks, Boonin! (17)


This article has explained what the substance view of personhood is. It explained Boonin’s objections and evaluated them. It then went on to show how Boonin himself ends up using a form of the substance view to ground human rights. In conclusion, it seems that human nature is the best grounds for human equality and rights. And since the unborn share the same human nature as the rest of us, they should be given equal rights and not be killed.


  1. Scott Klussendorf, The Case for Life: Equipping Christians to Engage the Culture (Wheaton, IL: Crossway, 2009), 50.
  2. This list is given by Mary Anne Warren in her article “On the Legal and Moral Status of Abortion” found in Jonathan Wolff’s Readings in Moral Philosophy (New York, NY: W. W. Norton and Company, 2018), 346.
  3. Klussendorf, The Case for Life, 54. Uses Robert P. George’s “Cloning Addendum” National Review Online, July 15, 2002.
  4. Trent Horn, Persuasive Pro-Life: How To Talk About Our Culture’s Toughest Issue (El Cajun, CA: Catholic Answers Press, 2014), 130.
  5. Horn, Persuasive Pro-Life, 131.
  6. Stephen Schwarz, The Moral Question of Abortion (Chicago, IL: Loyola University Press, 1990), 101. Quoted in David Boonin, A Defense of Abortion (Cambridge, EN: Cambridge University Press, 2003), 23.
  7. Boonin, A Defense of Abortion, 24.
  8. Boonin, A Defense of Abortion, 24.
  9. Boonin, A Defense of Abortion, 25.
  10. Klussendorf, The Case for Life, 54.
  11. Boonin, A Defense of Abortion, 24. 
  12. Stephanie Gray, Love Unleashes Life: Abortion and the Art of Communicating Truth (Toronto, ON: Life Cycle Books, 2016), 48-49.
  13. Boonin, A Defense of Abortion, 115, 125-126.
  14. The dialogue is my own. But it follows Boonin’s argument in A Defense of Abortion, 121-124.
  15. Again, the dialogue is my own but the story and the imagined response comes from Francis J. Beckwith, Defending Life: A Moral and Legal Case Against Abortion (Cambridge, EN: Cambridge University Press, 2007), 147-148.
  16. Beckwith, Defending Life, 148.
  17. Paul Chamberlain is a professor at ACTS Seminary with his Ph.D. in philosophy and a good friend of mine. We spent a good three hours looking over this article and he gave me this suggestion.
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Born in Vancouver, B.C., Chris has been married to Amy since 2017. He has a BA in Religious Studies (Youth Leadership), and an MA in Theological Studies (Apologetics). He enjoys acting, evangelism, and debates.

The views and opinions expressed in these articles are those of the author and do not necessarily reflect the official position of Human Defense Initiative.