Responses to Anti-Abortion Arguments

1.“All people are human organisms, therefore, all human organisms are people.”

Some anti-abortion advocates use this thinking to justify their belief that all abortions are immoral.

The argument that “all A are B, therefore, all B are A” is NEVER valid logic. This type of argument is a logical fallacy called “illicit conversion.”

Consider the following statement: "All poodles are dogs; therefore, all dogs are poodles." This statement is false because there are other types of dog breeds besides the poodle, like Golden Retriever, Labrador, and German Shepherd. The illogical conclusion that “all dogs are poodles” came from the mistake of making a bad inference, or in other words, from assuming something is true without proof that backs up the assumption. The illicit conversion fallacy is closely related to another fallacy called “affirming the consequent.”

Valid logic works like this:

          If A, then B.


          Therefore B.

          Ex. If it is a poodle, then it is a dog.

          Rex is a poodle.

          Therefore, Rex is a dog.

          (This is logical.)

The affirming the consequent fallacy happens like this:

          If A, then B.


          Therefore A.

          Ex. If it is a poodle, then it is a dog.

          Rex is a dog.

          Therefore, Rex is a poodle.

          (This is illogical.)

Like the affirming the consequent fallacy, the Illicit conversion fallacy happens when people assume the converse of a statement is true without proof. If you do not watch out for these fallacies, you may find yourself believing absurd conclusions like “all dogs are poodles.”

Let’s look at a tricky example: “All triangles are three-sided polygons, therefore, all three-sided polygons are triangles.” You can immediately be assured that this statement is NOT TRUE because any statement in the form “all A are B, therefore, all B are A” is never a valid logical statement. Proving that a pair of converse statements (“all A are B” and “all B are A”) is true requires knowing the exact definition of “A” and the exact definition of “B.” While the two statements within this tricky example, “all triangles are three-sided polygons” and “all three-sided polygons are triangles,” are actually BOTH TRUE, they are only true because the definitions of polygon and triangle support them. The definition of a polygon is a closed 2D figure, without concavity, made from connected straight line segments. The definition of a triangle is a polygon with exactly three sides. It is only because we know these two definitions that we can affirm both “all triangles are three-sided polygons” and “all three-sided polygons are triangles” are true statements. A statement like “all three-sided polygons are triangles” is never true simply because the converse, “all triangles are three-sided polygons,” is true, and vice versa. Proving both statements are true is a different logical process than proving one statement is a logical conclusion from another.

Okay, so now let’s look at the anti-abortion argument that “All people are human organisms, therefore, all human organisms are people.”

First, this argument’s format is that of the illicit conversion fallacy, which means the argument is automatically false. We can never logically conclude “all B are A” based on the statement “all A are B” being true, therefore, we can never logically conclude “all human organisms are people” based on the statement “all people are human organisms” being true.

The statement “all people are human organisms” is generally accepted as true by society. Not all members of our society believe it is true though, like philosophers who consider the possibility that aliens or artificial intelligence could be people and like animal rights activists who consider that denying personhood to all non-human organisms is speciesist. For the sake of time and to not get too far off-topic, we are going to hypothetically let the statement that “all people are human organisms” stand as true.

As aforementioned, to believe “all human organisms are people” based on the statement “all people are human organisms” being true is fallacious logic. The only way to know whether the statement “all human organisms are people” is true or not is to know and compare the definitions for “human organism” and “person.”

In the abortion debate, the definition of “human organism” is not a strong point of contention. An organism is a living being that meets the seven criteria for biological life and exists as a relatively unique individual. Human organisms are multicellular organisms that have human DNA in their cells.

The definition of “person” on the other hand, is much more contentious. On our First Question page, we review philosophy's most well-known definitions of person. Then we note that none of those definitions have been able to satisfy enough Americans to resolve the abortion debate. Because necessity is the mother of all inventions, and because our society needs an agreeable definition for person to resolve the abortion debate, Respect People coined a new definition for person: the Ten Criteria for Human Personhood, which are the seven criteria for biological life, plus three additional criteria specific to human people: human genetic code, the ability to think thoughts, and the ability to feel emotions. The Ten Criteria for Human Personhood were carefully devised to not exclude infants, disabled people, or unconscious people (those who tend to be excluded in certain problematic definitions for personhood) while at the same time devised to purposely exclude individual human cells (which were problematically counted as people by Noonan’s genetic criterion).

Some people argue that Noonan's genetic criterion does not actually count cells as people because "Noonan claims that human beings are people with a right to life, and human cells aren't human beings."

Let's set the record straight with logic.

First, the definition of the noun "being" is "a living thing" (Merriam-Webster). It's true that the noun "being" is often used colloquially to reference a person (living people are undoubtedly human beings), but people are not the only things that qualify as beings.

Based on the definition of being, the following premise is true:

If something is a living thing, then it is a being.

Now for some logic (modus ponens):

          If something is a living thing, then it is a being.

          A cell is a living thing.

          Therefore, a cell is a being.

The premise is true, and the logic is valid, therefore the conclusion that a cell is a being is true.

Cells are beings.

Human cells are human beings. 

Record is now set straight.

As for Noonan's genetic criterion, his exact words were "A being with a human genetic code is man" (57).

Consequently, the following is true:

Noonan's genetic criterion counts beings with a human genetic code as people with a right to life.

Human cells are beings with a human genetic code.

Therefore, Noonan's genetic criterion counts human cells as people with a right to life.

In sum, Noonan's genetic criterion is an unacceptable definition of person.

The moral of the story of Noonan's stance on abortion is that conflating the biological labels "human" and "humanity" with the philosophical labels "person" and "personhood" leads to illogical conclusions. One wonders if Noonan purposefully conflated the terms to artificially strengthen his argument. Biological labels name properties of the observed world, while philosophical labels imply meaning to that which they describe. The question Noonan proposed for abortion—"How do you determine the humanity of a being?"—is duplicitously redundant. Of course all human beings, from cells (the smallest units of life) to organisms (more complex units of life), have humanity simply because they have human DNA. That's why they are called human beings and not fish beings or bird beings. The proper, accurate, non-duplicitous question that needed to be asked is, "How do you define a person?"

If the premise "all human organisms are people" is based on Noonan's unacceptable definition of person, then it is a false premise.

If you accept the Ten Criteria for Human Personhood as a fair definition of person, then it is also evident that the statement "all human organisms are people" is a false premise.

The only way the premise "all human organisms are people" could be true is if someone devised a new, acceptable definition of person that supported the premise. In the meantime, the belief that "all abortions are immoral because all human organisms are people" is not justified and thus does not belong in American law.

In anticipation of any future definition of person devised to support the belief that "all abortions are immoral because all human organisms are people"—and to challenge the Ten Criteria for Human Personhood—we earnestly ask, to judge the acceptability of the new definition: What is the motivation behind legally forcing people to treat a living thing that does not have the ability to think thoughts or feel emotions as a person? If your answer is potentiality, read response #2 below. If you have a different, serious answer, please click here to tell us about it. (To all the memers out there, yes, we already know about this meme.)


In his publication "I Was Once a Fetus: An Identity-Based Argument Against Abortion" from 2001, Philosopher Alexander Pruss claims "since I was a fetus, that fetus was I" (Introduction). While we wholly agree with Dr. Pruss that "all persons have a right-to-life," the statement on which his anti-abortion argument hinges—"since I was a fetus, that fetus was I"—is merely another illicit conversion fallacy written in the past-tense.

2. "A zygote has high potentiality. A zygote will become a person, therefore, a zygote is a person."

The potentiality argument against abortion was first described by the influential, devout Catholic philosopher and judge, John T. Noonan Jr. in his book, The Morality of Abortion: Legal and Historical Perspectives, published in 1970. 

Here is the excerpt relevant to this critique:

"Moral judgments often rest on distinctions, but if the distinctions are not to appear arbitrary fiat, they should relate to some real difference in probabilities. There is a kind of continuity in all life...But once spermatozoon and ovum meet and the concepts is formed, such studies as have been made show that roughly in only 20 percent of the cases will spontaneous abortion occur. In other words, the chances are 4 out of 5 that this new being will develop. At this stage in the life of the being there is a sharp shift in probabilities...It may be asked, What does a change in biological probabilities have to do with establishing humanity? The argument from probabilities is not aimed at establishing humanity but at establishing an objective discontinuity which may be taken into account in moral discourse...Would the argument be different if only one out of ten children conceived came to term? Of course this argument would be different. This argument is an appeal to probabilities that actually exist, not to any and all states of affairs which may be imagined" (55-56).

First, for "such studies" on the prevalence of spontaneous abortion (aka miscarriage), Noonan cites page 197 of Gregory Pincus's The Control of Fertility, published in 1965. Since 1965, the statistics for the prevalence of spontaneous abortion have changed from roughly 20 percent to roughly 70 percent. To use Noonan's own words, because we now know 'only three out of ten children conceived come to term,' the argument is indeed 'different.' The potentiality argument against abortion in 2021 is only 3/8th as strong as it was in 1970.

Second, if we anchor the potentiality argument with probability, as Noonan did, and if we use up-to-date statistics, then "A zygote has high potentiality. A zygote will become a person, therefore, a zygote is a person" changes to "A zygote has low potentiality. A zygote won't become a person, therefore, a zygote isn't a person."

Following this, some people ask, "What is the potentiality of a fetus that meets the Ten Criteria for Human Personhood?" Well, on the First Question page, we deduce that a fetus attains the Ten Criteria between 23 and 27 weeks gestation (inclusive). The spontaneous abortion rate of a fetus at or beyond 20 weeks (technically called "fetal demise rate" or "stillbirth rate") is less than 0.5 percent, which means the probability that a fetus that meets the Ten Criteria for Human Personhood will develop to term is greater than 99.5 percent. Thus, a fetus that meets the Ten Criteria for Human Personhood has very high potentiality.

A third issue with the potentiality argument against all abortions is that it does not take into account the cost of bringing a zygote's potential to fruition. That cost is pregnancy and delivery, both of which cause undeniable pain and suffering for a pregnant person and can be hazardous to their life and health. For use in moral discourse, the potential moral value of a zygote, embryo, or fetus ought to be weighed against the potential cost.

Furthermore, the potentiality argument against abortion stems from a philosophical argument called the "trajectory argument." Philosopher Don Berkich proved in his 2007 publication "A Fallacy in Potentiality" that applying the trajectory argument to uphold the claim that most abortions are immoral is unsound because doing so hinges on an illicit generalization.

For example, consider the trajectory argument: "You wouldn't have existed if your mom had an abortion, so abortion is wrong."

This argument implies that anything that prevents your existence is bad. The people who use this argument also typically hold the belief that abstinence is good, but by their own reasoning, if your mom had been abstinent, you wouldn’t have existed either.

Because of this contradiction, the implication that "anything that prevents your existence is bad" is an illicit generalization that undermines the validity of arguments that use potentiality to negate the morality of most abortions.

Overall, when you consider up-to-date statistics on spontaneous abortion and the potential cost of bringing a zygote's potential to fruition, the actual potentiality of a zygote is much lower than what those who argue the potentiality argument would have you believe. Consequently, the potentiality argument is not a strong argument against most abortions. To again use Noonan's own words, the belief that a zygote is a person appears 'arbitrary fiat' because it is not supported by 'probabilities that actually exist.' And on the whole, none of that really matters because the potentiality argument against most abortions is a fallacious form of the trajectory argument.

3.“Abortion is unnatural.” (Meaning: “The desire to kill one’s own children is unnatural.”)

First, this argument is an appeal to “what is natural,” implying that all that is natural is good. Such an appeal is problematic because not all that is natural is good. Natural poisonous plants, like oleander, can be hazardous to our health. Natural weather phenomena, like tornadoes and earthquakes, can also be hazardous to our health. For people with a uterus, natural pregnancy can be hazardous to their health (pregnancy complications are the sixth leading cause of death for women in the United States between the ages of 15 and 34).

Second, in nature, animals do sometimes kill their own children, especially when the children are sick or have deformities. This is a morbid topic, but if you'd like to learn more, see:

Ultimately, as explained on the First Question page, an unborn child does not exist until the 23rd to 27th week of gestation, which means elective abortion before 23-27 weeks gestation cannot be the moral equivalent of killing children.