1. Abortion defined:

The pro-life argument (syllogism) defines abortion as the intentional killing of an innocent human being.

That abortion intentionally kills a living human fetus is affirmed by many defenders of abortion:

• Abortionist Warren Hern in “What About Us?” — “We have reached a point in this particular technology [D&E abortion] where there is no possibility of denying an act of destruction. It is before one’s eyes. The sensations of dismemberment flow through the forceps like an electric current.”
• Feminist Camille Paglia in “Fresh Blood for the Vampire” — “Hence I have always frankly admitted that abortion is murder, the extermination of the powerless by the powerful. Liberals for the most part have shrunk from facing the ethical consequences of their embrace of abortion, which results in the annihilation of concrete individuals and not just clumps of insensate tissue.”
• Former SCOTUS justice Anthony Kennedy in Stenberg — “The fetus, in many cases, dies just as a human adult or child would: it bleeds to death as it is torn from limb to limb….The fetus can be alive at the beginning of the dismemberment process and can survive for a time while its limbs are being torn off….Dr. [Leroy] Carhart [the abortionist who challenged Nebraska’s partial“birth ban] has observed fetal heartbeat . . . with “extensive parts of the fetus removed,”…and testified that mere dismemberment of a limb does not always cause death because he knows of a physician who removed the arm of a fetus only to have the fetus go on to be born “as a living child with one arm.” At the conclusion of a D&E abortion…the abortionist is left with “a tray full of pieces.”
• Ronald Dworkin in Life’s Dominion — Abortion “deliberately kills” a developing embryo and “is a choice for death.”
• Naomi Wolf in “Our Bodies our Souls” — “Clinging to a rhetoric about abortion in which there is no life and no death, we entangle our beliefs in a series of self-delusions, fibs and evasions. And we risk becoming precisely what our critics charge us with being: callous, selfish and casually destructive men and women who share a cheapened view of human life…we need to contextualize the fight to defend abortion rights within a moral framework that admits that the death of a fetus is a real death.”

That the human fetus killed is a living human being is affirmed by many defenders of abortion:

• California Medicine op-ed (1970) — “Since the old ethic has not yet been fully displaced it has been necessary to separate the idea of abortion from the idea of killing, which continues to be socially abhorrent. The result has been a curious avoidance of the scientific fact, which everyone really knows, that human life begins at conception and is continuous whether intra-or extra-uterine until death. The very considerable semantic gymnastics which are required to rationalize abortion as anything but taking a human life would be ludicrous if they were not often put forth under socially impeccable auspices. It is suggested that this schizophrenic sort of subterfuge is necessary because while a new ethic is being accepted the old one has not yet been rejected.”
• David Boonin in A Defense of Abortion — “A human fetus, after all, is simply a human being at a very early stage in his or her development.” As we will see, Boonin argues for abortion anyway. But he concedes that you are identical to the embryo/fetus you once were. You are the same human being today as you were then.
• Peter Singer in Writings on an Ethical Life — “Whether a being is a member of a given species is something that can be determined scientifically, by an examination of the nature of the chromosomes in the cells of living organisms. In this sense, there is no doubt that from the first moments of its existence an embryo conceived from human sperm and eggs is a human being.”

That the human fetus is innocent means it does nothing to warrant intentional killing. Its innocence is confirmed by its age and development: At that stage, it cannot desire evil or harm, only present its need to be sustained.

From all sources above, abortion is defined as the intentional killing of an innocent human being.

Finally, visual evidence confirms that abortion intentionally kills innocent humans:

• Justification for abortion images: They reawaken moral intuitions and convey truths in ways that words alone cannot. Examples include movies like Schindler’s List, Hacksaw Ridge, and The Passion of the Christ. Likewise, few complain when professors use grisly imagery from World War 2 or the Vietnam War as adjuncts to lecture material. Intellectual honesty requires we teach the abortion controversy with no less academic rigor.
• Frederick Douglass (black abolitionist) in his immortal speech “What to the Slave is the Fourth of July?” confronted critics who said reasoned arguments were enough to end slavery. According to Douglass, the slavery debate had been won on the level of reasoned argument, but the public had yawned. To awaken the moral conscience of the nation, “it is not light that is needed, but fire; it is not the gentle shower, but thunder.” Douglass was absolutely right. The practice of slavery was not sustained by reasoned arguments, but by slaveholders’ desire for self-preservation and non-slaveholders’ apathy or inactivity. The battle to be fought wasn’t a battle of ideas — that battle already had been won — but a battle of conscience. A decade later, abolitionist circulated gruesome photographs depicting the inhumanity of chattel slavery. The pictures helped galvanize anti-slavery sentiment in the North. The same, I submit, is true of the abortion debate today. Millions of Americans will tolerate abortion as long as they never see abortion.
• I realize that some may object to abortion-victim images on grounds that they substitute emotion for reason and therefore should not be used in public presentations. But this objection misses the point entirely. The question is not, Are the pictures emotional?. They are. The real question is, Are the pictures true?. If so, they ought to be admitted as evidence. We ought to avoid empty appeals to emotion, those offered in place of good reasons. If, however, the pictures substantiate the reasons I am offering and do not obscure them, they serve a vital purpose. Truth is the issue.
• This is precisely the point feminist Naomi Wolf made on abortion imagery in her article “Our Bodies, Our Souls” — “The pro-choice movement often treats with contempt the pro-lifers’ practice of holding up to our faces their disturbing graphics….[But] how can we charge that it is vile and repulsive for pro-lifers to brandish vile and repulsive images if the images are real? To insist that truth is in poor taste is the very height of hypocrisy. Besides, if these images are often the facts of the matter, and if we then claim that it is offensive for pro-choice women to be confronted with them, then we are making the judgment that women are too inherently weak to face a truth about which they have to make a grave decision. This view is unworthy of feminism.”

Main point: Pro-lifers correctly say that abortion intentionally kills an innocent human being.