PHIL 2030: Introduction to Ethics
Dr. Robert Lane
Lecture Notes: Monday October 13, 2014


[6.2.] Why is Killing a Fetus Wrong?


Having explained his theory of the wrongness of killing (see previous lecture notes), Marquis proceeds to use that theory in his FLO (“Future-Like-Ours”) argument that most abortions are immoral.


According to Marquis, killing a fetus deprives the fetus of an FLO, just like killing an adult human being deprives him or her of an FLO.  For example, if it is now wrong to kill a 20-year-old (let’s call him Bill) because it would deprive him of an FLO, then it would have been wrong to kill Bill when he was a fetus.


Just like Bill now, Bill-as-a-fetus had an FLO. In fact, Bill-as-a-fetus had the exact same FLO as Bill-as-a-20-year-old. That future is shorter when Bill is a 20-year-old, but it is still the same future that he had when he was a fetus.


This is true even if Bill-as-a-fetus was not a person and even if Bill-as-a-fetus was not conscious. Marquis’s argument does not depend on the assumption that fetuses are persons, or that they are conscious, or that they have souls, etc.


Here is one possible formulation of Marquis’s FLO Argument:


1.      If killing a being will deprive it of an FLO, then it is prima facie immoral to kill that being.

2.      Killing a fetus deprives it of an FLO.

3.      Therefore, it is prima facie immoral to kill fetuses. [supposed to follow from 1 and 2]

4.      In the vast majority of abortions, there are no other moral considerations that trump the prima facie obligation not to kill a fetus.

5.      Therefore, the vast majority of abortions are immoral. [supposed to follow from 3 and 4]


About Marquis’s use of the word “fetus”: Sometimes the word “fetus” is used in a narrow sense, to refer only to pre-birth humans during and after the ninth week of pregnancy. But Marquis is using the word “fetus” in a broader sense, to mean a pre-birth human from around day 14 after conception to birth.


Why around day 14? One reason may be that by that time, twinning is definitely no longer possible. Twinning is the division of a single pre-birth human into two, resulting in identical twins (as opposed to fraternal twins, which result from the separate fertilization of two different ova by separate spermatozoa). Although he doesn’t say so explicitly, it seems that Marquis intends his account to apply only after the embryo can definitely no longer split to become identical twins.[1]


Another relevant fact, which Marquis may not have had in mind (since it has come to light only relatively recently): it is possible for two separate pre-embryos (resulting from two separate conception events) to fuse into a single pre-embryo having two different genomes. (Had they not fused, they would have developed into fraternal twins.) The humans resulting from this sort of pre-implantation fusion are called chimeras.[2]


Marquis is arguing that abortion is prima facie immoral:

·         The conclusion of his argument leaves room for special cases in which the obligation not to kill a fetus might be overridden (e.g., cases in which the mother’s life would be threatened by bringing the fetus to term).

·         But the fact that there are such special cases does not mean that abortion, in general, is morally acceptable. Marquis believes that in the vast majority of cases, abortion is morally wrong.



·         Is the first step of the argument (from 1 and 2 to 3) valid? [yes]

·         Is the second step (from 3 and 4 to 5) valid? [yes]

·         Are the premises true? [1, 2 and 4?] – I am leaving this an open question… you should form your own opinions about whether each of these premises is true.



Stopping point for Monday October 13. For next time, begin reading Thomson, “A Defense of Abortion” – read RTD pp.88-92 (up until the end of section 1).



[1] I believe this is what he has in mind when he says that “morally permissible abortions will be rare indeed unless, perhaps, they occur so early in pregnancy that a fetus is not yet definitely an individual.” (RTD 91; in original article on p.194; emphasis added). He mentions the 14-day point in a later statement of his FLO argument: he describes his position as being that abortion is wrong, except perhaps in rare instances, e.g. “abortion during the first fourteen days after conception when there is an argument that the fetus is not definitely an individual.” “An Argument that Abortion is Wrong,” in Ethics in Practice, ed. Hugh LaFollette. Cambridge, MA: Blackwell, 1997, 91-102, p.91, emphasis added. See also a revised version of “Why Abortion is Immoral” which appears in Morality in Practice, 6th ed., ed. James Sterba, pp.125-9, where Marquis writes that he is setting aside considerations that suggest that abortion may be moral “before implantation”, which occurs during the second week after conception.

So far as I have been able to discover from embryology texts, twinning can actually occur only as late as day nine, and at that point the twins are at risk of being conjoined. (Scott Gilbert et al., Bioethics and the New Embryology, p.16)]


[2] Human chimeras, resulting from pre-implantation fusion and other means, are now believed to be more common than was previously thought. See Carl Zimmer, “DNA Double-Take,” New York Times, Sept. 16, 2013, URL = < >, retrieved October 13, 2014.

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