David Boonin is an associate professor of Philosophy at the University of Colorado at Boulder. In his book, A Defense of Abortion, Boonin attempts to argue from premises that pro-lifers accept to show that abortion is morally permissible. (1)

Boonin is aware of the continuity between an unborn and born child. He talks about how he has several pictures of his son Eli in his office. He describes a few of them and how Eli was a different age in each, then explains, “Through all of the remarkable changes that these pictures preserve, he remains unmistakably the same little boy.” [2] Finally he describes a sonogram taken of Eli weeks before his son was born and muses, 

“There is no doubt in my mind that this picture, too, shows the same little boy at a very early stage in his physical development. And there is no question that the position I defend in this book entails that it would have been morally permissible to end his life at this point.” [3]

It is a chilling admission but it’s also refreshing to hear such brutal honesty. Boonin is a serious, careful thinker, and his arguments deserve to be engaged with.

In this article, I will first summarize the five chapters of the book. In the second half, I will offer critiques of four select arguments.


Chapter 1

Boonin explains that there are two questions that are generally asked about abortion: “Is it moral or immoral?” and “should it be legal or illegal?” [4] He writes, 

“In principle, these are importantly distinct questions. There are actions such as jaywalking, which we may think to be justifiably illegal and yet not immoral, and there are actions, such as adultery, which we may think to be immoral and yet not justifiably illegal.” [5]

Boonin goes on to explain that for everyone to get on board with abortion, it would have to be shown to be morally justifiable. If it is seen as on par with murder, it is no surprise that people would be calling for it to be criminalized. [6] Boonin defines an action as morally permissible if “no one has a valid claim against my doing it, that doing it violates nobody’s moral rights.” [7] His thesis is that the fetus has no valid claims against the woman having an abortion because even though it is a human like his son through every stage of development, that is not enough to endow him or her with rights. [8]

To show this, he uses a method called reflective equilibrium.

“We begin by accepting, at least provisionally, our moral intuitions about a variety of types of actions, giving more initial weight to those which seem especially clear or forceful. We then attempt to develop a credible moral theory that would serve to unify and underwrite these various judgments.” [9]

He sees this as the exact approach used by critics of abortion when they attempt to show that if abortion is allowed in one case, it could lead down a slippery slope to killing infants in similar circumstances. [10]

Chapter 2

In Chapter 2, Boonin takes on the pro-life conception criteria.  He explains that the main idea behind the conception criteria is that  “you and I have this right, and that we are related to human fetuses in important ways in which we are not related to dogs, trees, ecosystems, and other possible objects of moral concern.” [11] He critiques nine different arguments to this effect but for the sake of space, I will focus on one that addresses, yet misunderstands, a very common pro-life argument. [12] 

Boonin tackles the parsimony argument which points to the fact that from fetus to adult, we are all members of the species homo sapiens. Boonin begins by rightly arguing that merely saying someone is a human being is not the same as showing they have a right to life. The second half needs justification. He goes on to a hypothetical scenario that a pro-lifer could use to make their case. Imagine there is a room where ten humans are placed together. Both sides agree that all these humans have a right to life. We could then ask what they all have in common. The answer is: their humanity. Therefore, the right to life should be grounded in their humanity. While Boonin agrees that on the surface this seems parsimonious, he ultimately rejects common humanity as sufficient grounds for the right to life. [13]

He adds to the story that a DNA test is done on all the people present and when the results come back, it turns out one of them is an alien from another planet. If the right to life is only based on being human, that would mean it would be okay to kill that alien visitor. [14] But, Boonin argues, 

“No matter what our views on abortion, it is extremely difficult to believe that this discovery would make us think it any more permissible to kill him. He has all the same properties we thought he had before; he simply got them from alien parents instead of human ones.” [15]

Boonin believes this hypothetical situation undermines the parsimony criteria.

Chapter 3

This chapter consists of two parts. The first is an attempt to rebut arguments that claim fetuses have human rights at other early stages of development: implantation, when the baby has human form, fetal movement, quickening, and initial brain activity. [16] I don’t think pro-lifers should even be presenting these arguments since they try to ground human rights in a stage of development and that is what we are trying to avoid. 

In the second part, Boonin lays out his argument for when he thinks human fetuses acquire the right to life: at the stage where organized cortical brain activity is present. He writes, 

“organized cortical brain activity refers to electrical activity in the cerebral cortex of the sort that produces recognizable EEG readings… there is no evidence to suggest that this occurs prior to approximately the 25th week of gestation, and ample evidence to suggest that it does begin to occur sometime between the 25th and 32nd week. If the onset of such activity marks the point at which the fetus acquires the right to life, then the vast majority of abortions do not involve the death of an individual with a right to life.” [17]

Why is cortical brain activity so important? Because Boonin believes that people are only worthy of moral consideration when they have desires about how their life should go. And they can only have desires when they are conscious. And they are not conscious before they have organized cortical brain activity. [18]. He writes, “It therefore has no such desires prior to the point at which it has organized electrical activity in its cerebral cortex. One implication of this account of the wrongness of killing, then, is that the fetus does not acquire the moral standing that you and I have prior to the point at which it has such activity.” [19]

Chapter 4

In chapter 4, Boonin switches gears. He grants that the fetus has a right to life at every stage of development for the sake of argument. [20] However, he uses Judith Jarvis Thomson’s violinist argument to show that abortion is still permissible even if unborn is a person with a right to life. The argument goes like this: 

One morning, you wake up in a hospital and find yourself attached by tubes to a violinist. The violinist is suffering from a fatal kidney disease and he needs a blood transfusion to stay alive. The Society of Music Lovers checked medical records and found out you were the right blood type. You are apologized to for the inconvenience, but also told that if you unplug yourself from him, he will die. But cheer up. In nine months, he will be able to survive without the use of your blood and you can go on your happy way! [21]

Most people would say that in this case, you are morally justified in unplugging yourself. But then, argue Thomson and Boonin, that shows that someone’s right to life does “does not include or entail the right to be provided by you with the use or continued use of whatever they need in order to go on living…” [22]

Boonin insists that it is not enough for the pro-lifer to show the fetus has a right to life. We must also show that, unlike the violinist, the fetus has a right to use the woman’s body. He believes there are three avenues through which the pro-life side can attack this argument. 1) Find a morally relevant difference between the two scenarios. 2) Bite the bullet and say that it is morally impermissible for the woman to unplug herself from the violinist. 3) Reject the authority of analogy. He sees the first option as the most popular tactic. [23]

Chapter 5

Finally, 5 Boonin tackles non-rights-based arguments. These include the golden rule argument, the culture of death argument, the pro-life feminist argument, and the uncertainty argument. (24)

Boonin has written an impressive book. It has certainly made me think hard about some of the arguments I have taken for granted as successful. From here I want to evaluate some of the key claims that his book makes.


Boonin and I agree on a number of points.

1) There is continuity in human beings through all stages of development. 

2) Saying something is immoral is not the same as saying it should be illegal.

3) Murder is something that is immoral and should be illegal.

4) It needs to be established that abortion is tantamount to murder. 

However, there are some issues with his arguments. Let’s begin by looking at his objections to the parsimony argument.

Response to the Parsimony Argument Rebuttal

Boonin believes that the parsimony argument claims the right to life is based on being human. But it is not. One of the main issues here is that Boonin separated the parsimony argument from what he calls the species essence argument, when in actuality they are closely tied together. (25) The parsimony argument is about basing the right to life on the nature (or species essence) which all humans share regardless of their stage of development. And the nature that they all share is personal. As Beckwith explains, “For the pro-life position is based on the personal nature of human beings and the presence of that nature from the moment a human being comes into existence regardless of whether it has the present exercisable capacity for, or is currently engaging in personal acts.” (26)

But that is not to say that only humans have a personal nature. There could be aliens like the one in Boonin’s story that also have a personal nature. And as Beckwith goes on to argue, “Consequently if another species exists, whether in this world or in another (such as Klingons and Vulcans of Star Trek lore), which possesses a personal nature from the moment any of its individual members comes into being, then pro-lifers would seek to have those creatures protected from unjustified homicide as well.” (27)

Boonin does respond to the “Substance view of Persons” argument in another section of the book. I have written a response to that elsewhere. You can read it here and find the link in the footnotes. (28) For now, we can move on to Boonin’s arguments based on cortical brain activity.

Response to Boonin’s Organized Cortical Brain Activity Criteria

There are two ways we can approach Boonin’s argument. First, we could demonstrate the logical absurdity of grounding the right to life in the development of cortical brain activity which ultimately has to do with the fetus’ stage of development. Philosopher Nancey Pearcey writes that the problem with making cognitive functions the standard is that “these characteristics emerge gradually. They are not traits that someone does or does not have. They are matters of degree—quantitative differences. What we do not find is a clear qualitative transition point for the momentous transformation from a non-person to a person.” (29) This opens up the possibility that the unborn already is a person when the abortion takes place and thus the Cortical Brain Activity Criteria is too tenuous to base something as valuable as human life on.

The other approach we can take is to show the logical issues that arise from grounding the right to life in desires. Pro-life apologist, Christopher Kaczor, asks us to imagine a Buddhist who believes that “extinguishing all desire is possible. If a human being achieved this goal, then this human being would have achieved Nirvana from a Buddhist perspective, but from Boonin’s perspective would thereby no longer have a right to life, since such a human being, the Buddhist Master, would have no desire for the future.” (30) I think even Boonin would admit that it would be absurd to say the Buddhist does not have a right to life in this case. But that raises the question of why it is not absurd to say the same about the unborn for the same reason.

Response to the Violinist Argument

That brings us to the violinist argument. When I first heard this argument, it threw me. I am definitely a pro-lifer who would tell the person who got plugged into the violinist that they were not required to use their body to keep that person alive. And of course, that led me to wonder, as the argument is meant to, “How can I then tell a woman that she’s required to be plugged into a baby for nine months just to keep him or her alive? If personhood and the right to life aren’t enough to grant the violinist the right to use someone else’s body against their will, why is it enough to grant it to the unborn?”

But this in turn made me start thinking about what we expect of parents in general. As Scott Klussendorf writes, “we may not have  the obligation to sustain strangers who are unnaturally plugged into us, but we do have a duty to sustain our own offspring.” [31] Scott B. Rae asks us to imagine a scenario where you and your spouse have a four-month-old baby in your house.

“The baby has not been sleeping for more than a couple of hours at any one time, and both of you are exhausted and desperately need a break. So you decide to take a two week vacation, just the two of you. But instead of making arrangements for the baby, you prepare enough bottles of formula for two weeks and you stack two week’s worth of diapers in the nursery. You then kiss your baby goodbye and leave. Upon your return, who do you think would be there to “greet” you? Angry neighbors, incensed relatives, Child Protective Services, and the police — all of those, and possibly others, would be very interested to see you on your return.“ [32]

As Rae argues, chances, are you’d be arrested for child negligence, maybe even infanticide because the baby died before anyone found him or her. [33] What this tells us is that if you’re a parent, your child has the right to expect you to look after his or her basic needs, even when it puts a strain on you that you’d rather not have.

So, the largest difference between the violinist and the unborn baby is that the woman has no parental obligations to the violinist.  Boonin acknowledges this but says “But it will count against the good Samaritan argument only if these obligations are generated by the mere fact of the biological relation between them.” [34) The biological connection is certainly part of it. But there are other considerations. 

One is the responsibility factor. All the woman who woke up plugged into the violinist did was go to bed. Klusendorf explains that going to sleep is not an action that leads naturally to her situation. Having sex on the other hand does naturally lead to pregnancy. Thus, the woman engaged in activity that created a life that is dependent on her. [35] Second, there is the fact that no one besides the woman could provide the baby with what they need at the earliest stages of their life. 

Boonin counters this first point by saying that the woman might be responsible for the fetus’ existence, but she are not responsible for the fact that it is needy. Furthermore, he argues that she is only required to lend someone the use of her body if she harmed the person and caused them to need it in the first place. [36]

Instead of trying to rebut his principle, I am going to grant it and see where it takes us.  Let’s go back to the scenario of the couple who abandons their child so that they can take a vacation.  They are responsible for the baby’s existence. But they’re not responsible for the fact that she needs them to stay home with her to survive. If Boonin is right and people only need to assist those who they are responsible for making needy in the first place, then there is nothing wrong with those parents leaving their child alone while they go on vacation. But the fact is, even pro-choicers would say that the parents are wrong to do that. What this shows me is that parents are still required to assist their child even if they did not cause them to be needy.

Boonin does not like analogies such as this. He thinks they beg the question. We’ve already decided as a society that born children have a right to be given the support of their parents. But “In the case of an unintended pregnancy, on the other hand, the question of whether the fetus has a right not to be deliberately deprived of the needed support the pregnant woman is providing for it is precisely the question at issue.” [37] But as Beckwith points out, this charge of question-begging would ultimately undermine Boonin’s and Thompson’s case because they both “present uncontroversial examples… to extract from them principles that may be applied in the controversial question of justifying abortion if the unborn is a person.” [38] I am simply using analogy to show the logical outcome of their principle that I detect. After all, ideas have consequences.

 A Response to his “Argument from Uncertainty” Rebuttal.

In the last chapter, Boonin addresses an issue that deserves mention: the uncertainty argument. Boonin cites various authors who have used it, then tries to summarize it himself: “The basic structure of the argument from uncertainty is clear. The argument cojoins the claim that we are uncertain about the moral status of abortion with a principle designed to govern moral choices made under such conditions of uncertainty. What is less clear, however, is just what, precisely, the principle appealed to is meant to say.” (39)

But this isn’t what the argument is saying at all. The argument from uncertainty is responding to pro-choicers who simply throw up their hands and say “We can’t be sure whether the unborn is a person.” Beckwith puts it simply, “if one is not sure that one is killing a moral subject, then one should not kill it.” (40) In other words, the uncertainty is about the nature of the unborn. The uncertainty is on the part of the pro-choicers, not the pro-lifers. And when such uncertainty exists, the moral status of abortion is not uncertain at all. It is wrong and we should err on the side of life. 

Boonin points out that there are many acts that we do that we are not a hundred percent sure about the moral permissibility of such as killing plants and animals. (41) He notes how there have been many arguments put forward for the right to life of both and then says “But critics of abortion will surely reject the view that we must accept the claim that plants and animals have a right to life because we cannot be certain that they do not.” (42) This may all be true, but it is also true that there are certain actions we will not take when we are not a hundred percent certain if a human life is at stake. As Horn writes, “After all, we wouldn’t blow up a building if we thought there could still be people inside.” (43)

Boonin also attempts a reductio against the uncertainty argument. He writes, “It would be worse, for example, to mistakenly accept the belief that mowing your lawn is not on par with mass murder if it turns out that mowing your lawn really is on par with mass murder, than to mistakenly accept the belief that mowing your lawn is on par with murder if it turns out that it really isn’t.” (44) Despite this uncertainty, people keep mowing their lawns. Here I want to note that his arguments seem to work really well when the subjects are non-human entities. However, along with Beckwith, I think the examples he chooses “downplay the moral magnitude of killing an innocent person when one admits that the arguments on all sides of the moral status of the being in question are so equally compelling that one is forced to an agnostic position on the matter.” (45)

Boonin suggests that people might appeal to probabilities to show abortion is unjustified. He writes, “It is difficult to know precisely how you are supposed to determine the probability that your belief that abortion is permissable is mistaken in the first place, but it is even more difficult still to see why the probability should be significantly higher than the probability that your belief that killing plants and animals is permissable is mistaken.” (46) But pro-lifers would actually say that probabilities, whether high or low, are irrelevant in this case. Going back to the example of someone blowing up a building, Beckwith writes, “Even if the odds were 1 in 100, it would seem incredible that anyone would even consider the risk of murdering another human being so insignificant that she would take the chance.” (47) In short, pro-lifers are trying to appeal to common sense but Boonin seems to be trying to move the argument into the realm of anything but. 

Boonin finally raises the question of whether such reasoning would force us to also grant a prima facie right to life to human cells and unfertilized eggs. After all, cells can be used for cloning. And if parthenogenesis comes into a play, an unfertilized egg could potentially start developing into a human being. In other words, since both have the potential to become human persons like the fetus, shouldn’t we take measures to protect them as well? (48) 

In short, my answer is no. Again, this argument from uncertainty only applies to when we are uncertain if a human person is present. Until that cell is stimulated by the cloning process, (49) or we see the egg start dividing like in parthenogenesis, (50) then neither are whole organisms but “merely part of larger human organisms” as Klussendorf argues. (51) In other words, there is no human life at all and therefore, no reason to think a person is present. 

There might still be a good argument against the argument from uncertainty but Boonin has not presented them in this book. (46)


In this article, I began by summarizing David Boonin’s arguments. I then analyzed them. He gave a valiant effort to meet the critics of abortion halfway, and discuss these issues based on terms they would accept. However,  he was often mistaken about what some of the arguments were. Moreover, his criteria for what grounds human rights lead to certain absurd conclusions. His violinist argument does not provide sufficient grounds for abortion. For those reasons, his defense of abortion does not work. 


1. David Boonin, A Defense of Abortion (Cambridge EN: Cambridge University Press, 2003), 

2. David Boonin, A Defense of Abortion (Cambridge EN: Cambridge University Press, 2003), xiii.

3. Boonin, A Defense of Abortion, xiv.

4. Boonin, A Defense of Abortion, 3-4.

5. Boonin, A Defense of Abortion, 4.

6.  Boonin, A Defense of Abortion, 4.

7. Boonin, A Defense of Abortion, 5.

8. Ibid.

9. Boonin, A Defense of Abortion, 9-10.

10. Boonin, A Defense of Abortion, 13.

11. Boonin, A Defense of Abortion, 19.

12. Boonin, A Defense of Abortion, 19-90

13 Boonin, A Defense of Abortion, 20-22.

14. Boonin, A Defense of Abortion, 22.

15. Boonin, A Defense of Abortion, 22-23.

16. Boonin, A Defense of Abortion, 91-115.

17. Boonin, A  Defense of Abortion, 115.

18. Boonin, A Defense of Abortion, 125-126.

19. Boonin, A Defense of Abortion, 126.

20. Boonin, A Defense of Abortion, 133.

21. Boonin, A Defense of Abortion, 135.

22. Boonin, A Defense of Abortion, 138.

23. Boonin, A Defense of Abortion, 138.

24. Boonin, A Defense of Abortion, 282-324.

25. Boonin, A Defense of Abortion, 23-25.

26. Francis J. Beckwith, Defending Life: A Moral and Legal Case Against Abortion Choice (Cambridge, EN: Cambridge University Press, 2007), 161-162.

27. Beckwith, Defending Life, 162.

28. Chris Christiansen. “A Substantive Argument: A Response to David Boonin’s Critique of the Species Essence Argument.” (accessed May 2nd, 2022).

29. Nancy R. Pearcey, Love Thy Body: Answering Hard Questions about Life and Sexuality (Grand Rapids, MI: Baker Books, 2018), 53

30. Christopher Kaczor, The Ethics of Abortion: Women’s Rights, Human Life, and the Ethics of Abortion (New York, NY: Routledge Taylor and Francis Group, 2015),  62. (Kindle edition.)

31. Scott Klussendorf, The Case for Life: Equipping Christians to Engage the Culture (Wheaton, IL: Crossway, 2009), 188.

32. Scott B. Rae, Introducing Christian Ethics: A Short Guide to Making Moral Choices (Grand Rapids: Zondervan, 2016), 76.

33. Rae, Introducing Christian Ethics, 76.

34. Boonin, A Defense of Abortion, 234.

35. Klusendorf, The Case for Life, 189.

36. Boonin, A Defense of Abortion, 174-175. He has a long complicated example to prove this point but that is what the principle comes down to. 

37. Boonin, In Defense of Abortion, 168.

38. Beckwith, Defending Life, 185.

39. Boonin, A Defense of Abortion, 311.

40. Beckwith, Defending Life, 150.

41. Boonin, A Defense of Abortion, 314.

42. Boonin, A Defense of Abortion, 314.

43. Horn, Pro-Life Answers, 122.

44. Boonin, A Defense of Abortion, 315. 

45. Beckwith, Defending Life, 150. 

46. Boonin, A Defense of Abortion, 315.

47. Beckwith, A Defense of Abortion, 151.

48. Boonin, A Defense of Abortion, 316-318.

49. Beckwith, Defending Life, 161.

50. Boonin, A Defense of Abortion, 318.

51. Klussendorf, The Case for Life, 43.

52. As a side note, it is distressing to me and other philosophers that Boonin misrepresented this argument so badly. He says that this book came out of a series of lectures he gave at the University of Tulane. Boonin, A Defense of Abortion, xv. That means that, intentionally or not, he is passing on the straw men of the pro-life arguments to the various students he teaches. And unless they crack open a pro-life book, they won’t know any better. 

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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.