Concept

Pro-Life Premise-Based Argument

Intro

"Why is the unborn child a person who cannot be killed?"

This page gives the structured answer in plain steps. The argument runs in two parallel forms, a biblical one and a philosophical one, and both end at the same conclusion: the unborn human being has the same kind of moral protection that other human beings have.

The biblical version is simple and short.

Every human being is made in the image of God (Genesis 1:27) and therefore carries inherent dignity. The Bible treats the unborn as already known and shaped by God (Psalm 139:13-16, where the psalmist says "You knit me together in my mother's womb"). Scripture forbids the killing of innocent human life (Exodus 20:13). The unborn is innocent human life. Therefore the unborn cannot be intentionally killed.

The philosophical version does the same work without appealing to the Bible. It is the form to use with someone who does not share Christian assumptions.

The most useful tool is the SLED test, developed by Stephen Schwarz and Scott Klusendorf. SLED stands for the four differences someone might cite to deny that the unborn is a person:

Size. The unborn is smaller.
Level of development. The unborn is less developed.
Environment. The unborn is inside the womb, not outside.
Degree of dependency. The unborn depends on the mother.

The point of the SLED test is that none of these differences make a moral difference anywhere else. A small person is not less of a person than a tall one. A two-year-old is not less of a person than an adult. A baby inside a hospital and a baby outside it are equally persons. A person on dialysis or in intensive care is just as fully a person as one who is healthy. The same logic that protects the born from being killed for being small, undeveloped, in the wrong place, or dependent must also protect the unborn.

Don Marquis's "Future Like Ours" argument approaches the question from a different angle. What makes killing wrong is that it takes from a being a valuable future of experiences, projects, and relationships. The unborn has exactly that kind of future. Therefore killing the unborn is wrong for the same reason killing any other human being is wrong.

The substance-view personhood argument, developed by Patrick Lee, Robert P. George, Francis Beckwith, and Klusendorf, says a human being is the kind of being whose nature is personal from the start. A human embryo is not a potential person but a person with potential.

The page covers the biblical premises in detail, the philosophical arguments at length, the standard pro-choice objections (bodily autonomy, viability, sentience), and the responses to each.

In full

The structured biblical-philosophical case for the inviolable moral status of the unborn. The core deductive form has biblical and natural-law variants; the central claims are that (P1) every human bears the imago Dei and possesses inherent dignity, (P2) the unborn are biologically human from conception, therefore (C) the unborn bear the imago Dei and may not be intentionally killed. The biblical premises connect to Genesis 1.27, Psalms 139.13-16, Exodus 20.13, and Proverbs 31.8-9. The philosophical / natural-law form is most prominently developed in Don Marquis's "Future-Like-Ours" (FLO) argument (1989) and the substance-view personhood arguments of Patrick Lee, Robert P. George, Francis Beckwith, and Scott Klusendorf.

The biblical premise-based argument

As articulated in ris3n's note (Premise Based Argument, in the Pro Life note cluster):

P1. Every human being is created in the image of God and therefore has inherent dignity and value. Support: Genesis 1.27, "So God created mankind in his own image..."

P2. God's sovereignty extends to the life of every individual from conception. Support: Psalms 139.13-16, "For you created my inmost being; you knit me together in my mother's womb... Your eyes saw my unformed body."

P3. The Bible explicitly prohibits the taking of innocent human life. Support: Exodus 20.13, "You shall not murder."

P4. The Bible commands believers to protect and advocate for the vulnerable and voiceless. Support: Proverbs 31.8-9, "Speak up for those who cannot speak for themselves..."

Conclusion. Abortion is morally wrong because it violates the sanctity of life as established by God, contravenes God's sovereign creative agency in the womb, transgresses the biblical prohibition on the taking of innocent human life, and abandons the biblical command to protect the vulnerable.

Additional biblical texts commonly cited in this tradition: Jeremiah 1:5 ("Before I formed you in the womb I knew you"), Luke 1:41-44 (John the Baptist leaping in Elizabeth's womb at the Annunciation), Job 31:15, Isaiah 49:1, 5, Galatians 1:15.

The philosophical / natural-law arguments

The Future-Like-Ours (FLO) argument, Don Marquis

Don Marquis, "Why Abortion Is Immoral," Journal of Philosophy 86 (1989): 183-202.

P1. What makes killing an adult human wrong is that it deprives them of a "future of value", a future like ours, full of experiences, projects, activities, and enjoyments. P2. A normal human fetus has a future-like-ours of the same morally relevant kind. C. Therefore, killing a fetus is wrong for the same reason that killing an adult is wrong.

Marquis is non-religious and grounds the argument in secular ethics; the argument has had outsize influence in academic philosophy because it bypasses the personhood debate by relocating the wrong-making feature to "deprivation of valuable future."

The substance / endowment view

Patrick Lee, Robert P. George, Francis Beckwith, and others develop the position that human beings are substances of a rational kind from the moment of fertilization; the rational nature is endowed at the start of the substance's existence even when not yet exercised. The unborn is therefore not a "potential person" but an actual person with potential capacities. Key works:

Patrick Lee and Robert P. George, Body-Self Dualism in Contemporary Ethics and Politics (Cambridge, 2008); Conjugal Union: What Marriage Is and Why It Matters (Cambridge, 2014).
Patrick Lee, Abortion and Unborn Human Life (CUA Press, 1996; 2nd ed. 2010).
Francis J. Beckwith, Defending Life: A Moral and Legal Case Against Abortion Choice (Cambridge, 2007).

The SLED test, Scott Klusendorf

Klusendorf's pedagogical formulation: the differences between an embryo / fetus and a born human are reducible to Size, Level of development, Environment, and Degree of dependency, none of which are morally relevant differences justifying differential treatment.

Scott Klusendorf, The Case for Life: Equipping Christians to Engage the Culture (Crossway, 2009).

Major proponents and works

Don Marquis, "Why Abortion Is Immoral," Journal of Philosophy (1989); secular philosophical FLO argument.
Francis Beckwith, Defending Life (Cambridge, 2007); Politically Correct Death (Baker, 1993).
Scott Klusendorf, The Case for Life (2009); Pro-Life 101 (2002); founder of Life Training Institute. Pedagogically central in evangelical pro-life apologetics.
Patrick Lee, Abortion and Unborn Human Life (1996, 2010); substance-view personhood.
Robert P. George (Princeton), Embryo: A Defense of Human Life (with Christopher Tollefsen, 2008).
Christopher Kaczor, The Ethics of Abortion: Women's Rights, Human Life, and the Question of Justice (Routledge, 2011).
John Jefferson Davis, Abortion and the Christian (Presbyterian & Reformed, 1984); evangelical biblical-ethical treatment.
Pope John Paul II, Evangelium Vitae (1995); the Catholic magisterial articulation, drawing on Imago Dei and natural law.
Randy Alcorn, Pro-Life Answers to Pro-Choice Arguments (Multnomah, 2000).

Apologetic / theological deployment

The argument functions as the principal Christian response to the post-Roe v. Wade (1973; overturned in Dobbs, 2022) framework that frames abortion as a privacy / bodily-autonomy right of the pregnant woman. The pro-life response insists that:

The biological humanity of the unborn from fertilization is settled embryology, not religious dogma.
The moral status of the unborn cannot be downgraded by appeals to size, developmental stage, environment (in vs out of the womb), or dependency without committing the same logic to acceptance of infanticide and the killing of the severely disabled (the "expanding-circle" reductio).
Bodily-autonomy arguments (Judith Jarvis Thomson's "violinist," 1971) work, if at all, only for cases of rape; they do not justify the typical abortion case where the woman's choice contributed to the dependent's existence.
The biblical materials describe God as personally engaged with the unborn (Ps 139, Jer 1:5, Lk 1:41), pointing to personhood from conception or earlier.

Critiques and responses

The pro-choice / abortion-rights philosophical tradition contests the argument on several lines:

Personhood criteria. Mary Anne Warren, Michael Tooley, and Peter Singer ground personhood in actualized rationality / self-awareness / desires for continued existence; on these criteria, early embryos and fetuses (and arguably newborns) lack personhood. Pro-life response: these criteria are also satisfied by sleeping or comatose adults whom we still regard as persons; the criteria conflate person with functioning person.
Bodily autonomy. Judith Jarvis Thomson, "A Defense of Abortion," Philosophy & Public Affairs (1971), even granting personhood, the woman's right to her own body permits withdrawing life support. Pro-life response: bodily-autonomy arguments do not justify the direct killing of the fetus that abortion typically involves; pregnancy is not relevantly analogous to the violinist case (the moral weight of natural parental obligation; the typical contributory role of the mother's prior choice).
Future-of-value contests. Critics of Marquis (David Boonin, A Defense of Abortion, 2003) argue contraception also deprives a possible future of value, generating an unwanted reductio. Marquis-defenders respond that contraception does not deprive an actually existing entity of its future.
Hard cases (rape, severe fetal anomaly, threat to mother's life). Most pro-life thinkers acknowledge the threat-to-mother case as a genuine tragic conflict (often handled under the principle of double effect) and treat the rape case as the genuinely hard exception that, in their view, does not justify the broader abortion regime.
Old Testament passages sometimes deployed for a non-personhood reading (e.g., Numbers 5 supposed "abortion ordeal," Exodus 21:22-25) are vigorously contested in interpretation; ris3n's note addresses the Numbers 5 reading.