The lines of disagreement in the philosophical debate over abortion have never been clearer. While the politics of abortion remain as tumultuous and contested as they have ever been, the underlying philosophical, ethical, and scientific issues have been clarified to the extent that any careful person can examine the arguments of both sides and come to a principled and informed position.

This has not always been the case. Before the Supreme Court thrust the issue onto the national stage more than thirty-six years ago, pro-choice philosophers like Judith-Jarvis Thompson and pro-life philosophers like Germain Grisez were contributing to a debate that became more politically contentious even as the underlying scientific and philosophical issues were becoming clearer.

Consider the basic pro-life argument as it has developed over the last thirty years. Though there are many versions and several sophisticated philosophers who have made the case in more formal terms, the argument rests on three simple fundamental beliefs. The first is normative, the second medical or scientific, and the third is political.

The normative premise is that human life is a fundamental good and all human beings have a right to life. Some philosophers hold that this is a right not to be intentionally killed, though the killing of a human being may be accepted if it is the foreseen but unintended consequence of another justified action. Other philosophers do not completely rule out intending to kill a human being, but would take culpability and desert into account. Regardless, pro-lifers generally agree that unborn human beings have a right to life that cannot be violated.

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The scientific belief that ties into the normative premise is the simple medical fact that embryos and fetuses are human beings. There is no longer, strictly speaking, any debate about “when life begins.” That question has been answered not by religious authority but by the disciplines of human biology and embryology. A human life begins at the moment of conception when a distinct and complete, though immature, human being forms from the joining of her parents’ gametes.

What follows from the conjoining of the scientific and normative beliefs is disarmingly simple: all human beings have a right to life; unborn human beings are human beings; thus unborn human beings have a right to life. When you add the basic political belief that the purpose of governments and laws is to protect fundamental human rights, you arrive at the basic pro-life position.

The scientific component of the argument has become very clear over the last few years. No longer do we hear as much about “clumps of tissue” and the “products of conception” and other euphemistic attempts to obfuscate what is at stake in the abortion debate. Thanks to the remarkable advances in medical imaging technology, this scientific truth seems to be making inroads in the general public. When describing the realties portrayed in the ultrasounds pictures that now adorn millions of kitchen refrigerators, we refer to those creatures pictured by their names. They are not masses of tissue with the potential to be human; they are human beings, our sons and daughters, brothers and sisters, and grandchildren.

This clarifying advance in the scientific realm has also affected the normative debate. The argument is no longer about what sort of entity is killed during an abortion, but whether each human being, as a human being, has a right to life. Unlike the scientific consensus about when a human life begins, here the debate remains contentious, though the central dividing line is once again surprisingly simple.

Either one believes that all human beings as such have a right to life, or one believes that amongst the category of human beings some have a fundamental right to life and others do not. Hence the debate has shifted from determining when human life begins to when human personhood begins. This clarification of the debate is welcome and edifying, as Ryan Anderson illustrates with his account of just this sort of discussion at a recent event at Princeton.

Pro-choice philosophers differ amongst themselves about what qualities of a human being warrant the designation of human person, and when in the life cycle those qualities are salient enough to declare personhood. One such quality is the ability to feel pain, another is self-awareness, and yet a third is viability, or the capacity of the fetus to live outside the womb. Other pro-choice philosophers, however, take a different tack. They acknowledge a right to life for all human beings, but find other rights held by the mother to outweigh the right to life of the unborn human being. A mother, the argument might run, has a right to her own bodily integrity, or perhaps a right to make plans for the future autonomously. According to this line of thinking, such rights outweigh the real but secondary right to life of the fetus. Thus pro-lifers will refer to a fundamental right to life to distinguish their position from pro-choice advocates who acknowledge a right to life but believe it can be defeated.

Pro-life theorists often differ about political strategies and prudential tactical choices. They also differ amongst themselves as to the grounding of the normative claim that human life is a good. Some pro-lifers emphasize the religious underpinnings of the sacredness of life and the Judeo-Christian concept of imago dei; others do not necessarily hold such beliefs but start from the self-evident good of human life and leave theological considerations out of the public discussion. It is fair to say that pro-lifers generally agree on both the value of all human beings regardless of age and state of development and on the goal of seeing this value protected in law and cherished by the culture. They often disagree, however, on the argumentative and political means to achieve that end.

Nevertheless, the philosophical debate about the normative dimensions of the abortion issue still comes down to the aforementioned watershed difference: either human beings as such have a right to life, or some human beings have a right to life and are thus persons, and some are not and are thus expendable.

While pro-life philosophers must continue their work by applying principles to emerging bioethical questions, the argumentative clarity achieved by their work in the abortion debate has implications for pro-lifers who seek to continue to influence both the law and the culture. Perhaps the most important implication is also the most obvious. If the philosophical debate about abortion is over, the political debate remains.

What is needed now are pro-life thinkers and activists who have the intellectual chops to navigate the arguments and insights of the philosophers, the communication skills to translate them for both the pro-life rank-and-file and the persuadable middle, and the charisma and savvy to inspire and guide the pro-life movement. What we need, in other words, is more people like Scott Klusendorf and more books like his recently published The Case for Life: Equipping Christians to Engage the Culture (Crossway Books).

Klusendorf is president of the Life Training Institute and travels the country arguing for the pro-life cause. His book can perhaps best be described as a sort of bridge between the robust philosophical arguments of people such as Gerard Bradley, Francis Beckwith, and Robert P. George, and concerned citizens who care about abortion but are not going to trouble themselves with the distinctions between essential and accidental qualities of persons and mind-body metaphysical dualism. Klusendorf has a gift for explaining arguments without dumbing them down. It is not too much of a stretch to say that he has a bit of C.S. Lewis’s knack for taking what can be a complex-sounding issue and presenting in terms that regular people can understand. And, like Lewis, he often does this through helpful analogy and fictional, though entirely realistic, dialogue.

As the subtitle suggests, Klusendorf’s book is primarily written for Christians. Yet this should not be taken to suggest that the book is only written for religious believers. Many of Klusendorf’s arguments in the first three parts of the book apply to the pro-life movement as such and it is only in the fourth and last section that he devotes four chapters to the specifically Christian call to engage the culture for the sake of the unborn. His book is an invaluable resource that will reward the pro-life Christian and non-Christian alike, both for its substantive and winsome arguments about abortion and for its blueprint for influencing the culture with those arguments.

The short-term challenges for the pro-life community are as important as they are daunting given President Obama’s positive commitment to abortion and a compliant Congress. On the political front pro-lifers must continue to pursue prudent and commonsensical policies that restrict abortion at the state level. Parental notification, waiting periods, informed consent, and bans on particularly gruesome forms of abortion are worth defending and implementing. To borrow a sports analogy, hitting for singles and doubles has proven to be a more effective strategy than swinging for the home run that would be the repeal of Roe v. Wade.

At the federal level pro-lifers will be playing defense, given changed political realities. But even this shift can prepare for future success. It is telling that President Obama has had to back off his pledge to sign the Freedom of Choice Act, the pro-choice dream legislation that would codify Roe and transform abortion from a negative right that the government cannot fully obstruct to a positive right for which the government must provide the means. The pro-life movement must bring pressure to bear on these matters, expending political capital whether on high-profile legislation like FOCA or on more subtle attempts to achieve the substance of FOCA through executive orders and “add-on” language buried in more mundane legislation.

On the cultural level, pro-lifers must not shrink back from engaging the debate in a respectful and winsome manner in all venues and at all levels. Princeton professor Robert George sets an outstanding example in his discussion with Pepperdine University’s Doug Kmiec about abortion and the Obama administration. Of course not every conversation will achieve such a level of erudition, but the “everyday” conversations that will take place over the next few years will go a long way in determining whether ours will be a culture that values and protects life or a culture that continues to narrow the boundaries of what it means to be fully human.

Circumspection is prudent when confronted with claims that “now” is the crucial moment for a political movement’s success. Yet there are signs that the pro-life cause is making headway. Recent polling data is encouraging, if not definitive, and the changed language of the political discourse surrounding abortion is telling. For decades there have been tens of thousands of dedicated pro-lifers making a difference in schools, churches, and crisis pregnancy centers. Meanwhile pro-life academics have made the intellectual case for the unborn, often at personal and professional cost, and politicians and lawyers have fought for modest but successful protections in law and policy. Perhaps we are seeing some promising signs that these labors are bearing fruit in the attitudes of citizens throughout the culture.

In other words, this is not the time to shrink back from engaging the debate, whether in the Ivy League classroom, the factory lunchroom, or at the family reunion. Pro-life thinkers would do well to consider how to inspire and equip the average citizen who knows there is something terribly wrong with abortion, but isn’t sure how to think about the issue or address it with friends and family. Scott Klusendorf’s book is an excellent place to start.