Can Neuroscience Challenge Roe V. Wade? When I was asked this summer to serve as an expert witness in an appellate case that some think could lead to the next Supreme Court test of Roe v. Wade, I was surprised. Rick Hearn is the attorney representing Jennie McCormack, an Idaho woman who was arrested for allegedly inducing her own abortion using mifepristone and misoprostol - two F.D.A.-approved drugs, also known as RU-486 - and for obtaining the drugs from another state over the Internet. While the case against Ms. McCormack has been dropped for lack of evidence, Mr. Hearn, who is also a doctor, is pursuing a related suit against an Idaho statute, the "Pain-Capable Unborn Child Protection Act" (Idaho Code, Section 18-501 through 18-510), and others like it that cite neuroscientific findings of pain sentience on the part of fetuses as a basis for prohibiting abortions even prior to viability. The authors of a 2005 review of clinical research in the Journal of the American Medical Association have written, "Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester." Still, not surprisingly, opinions on whether and when fetal sensitivity to pain may develop vary widely. So why not call an actual neuroscientist as an expert witness instead of a scholar of the humanities? As Mr. Hearn explained, his suit challenges the government's use of results from the natural sciences, including neuroscience, as a basis for expanding or contracting the rights of its citizens. In this case, neuroscience is being used to expand the rights of fetuses by contracting the rights of women to choose whether to continue or terminate their pregnancies. In other words, a biological fact about women is being used by the state to force women to accept one societal role rather than another. Mr. Hearn approached me because of arguments I have made, including here in The Stone, that criticize the hubris of scientific claims to knowledge that exceeds the boundaries of what the sciences in fact demonstrate. The turn to legislation based on alleged neuroscientific findings in search of an end-run around the protections provided by Roe v. Wade is popular among Republicans. Mitt Romney voiced his strong support for such legislation in 2011, when he wrote in a piece in National Review, "I will advocate for and support a Pain-Capable Unborn Child Protection Act to protect unborn children who are capable of feeling pain from abortion." Since viability is, according to Roe v. Wade, the point at which the state's interest in protecting "the potentiality of human life" becomes compelling enough to override its interest in protecting the right of a woman to make decisions regarding her body and its reproductive organs, Idaho's statute and others like it would either be found unconstitutional or, if upheld, entail overturning a fundamental aspect of Roe v. Wade. For neuroscientific findings of fetal pain to serve as a basis for permitting states to prohibit abortion prior to viability, they must tell us something about the nature of a fetus that makes the state's interest in protecting it more compelling than its interest in protecting a woman's right to make basic decisions about her own body. As pain sentience does not serve as a basis for legal prohibitions in general (or else mousetraps and deer hunting would be prohibited), the statutes' real purpose is to use potential evidence of pain sentience in fetuses to indicate the presence of something far more compelling - namely, personhood. Those wishing to abolish abortion believe that "the fetus is a 'person' within the language and meaning of the Fourteenth Amendment." If, as Justice Harry A. Blackmun continues in his opinion in 1973, "this suggestion of personhood is established, the appellant's case, of course, collapses, for the fetus' right to life would then be guaranteed specifically by the Amendment." If a fetus is a person, in other words, then it is not a potential human life at all, but is a fully human life deserving of full legal protection, and abortion must be murder and punishable as such. The intent of current fetal pain statutes is, clearly, to infer from the ability to feel pain on the part of a human fetus - if it can be established by neuroscience - a claim for actual human life or full personhood. The implicit vehicle for this inference is the concept of consciousness. Nebraska's "Pain-Capable Unborn Child Protection Act," passed in 2010, for instance, not only refers to "ability to feel pain," it also characterizes the unborn child as "having the physical structures necessary to experience pain," and claims that the evidence shows that "unborn children seek to evade certain stimuli." It is obvious from the terms "experience" and "seek" that the statute's implicit understanding of the ability to feel pain is that "feeling" refers not merely to what neuroscientists call the nociceptive capacity of an organism - the ability of its nervous system to detect and respond to potentially noxious stimuli - but to conscious awareness of the presence of such stimuli. Current neuroscience distinguishes a spectrum of degrees of "consciousness" among organisms, ranging from basic perception of external stimuli to fully developed self-consciousness. Even the idea of self is subject to further differentiation. The neuroscientist Antonio Damasio, for instance, distinguishes degrees of consciousness in terms of the kind of "self" wielding it: while nonhuman animals may exhibit the levels he calls proto-self and core-self, both necessary for conscious experience, he considers the autobiographical self, which provides the foundations of personal identity, to be an attribute largely limited to humans. This more robust concept of consciousness that distinguishes human personhood from more basic forms of perception has a very specific history, which dates to the early 17th century and is most associated with the French philosopher René Descartes and the school of thinkers that followed him. While Descartes considered whether a neonate or even young children might have consciousness of this kind, in the end he rejected this hypothesis, insisting on the "reflective" nature of consciousness. As he writes in a letter responding to some objections voiced by Antoine Arnaud, "I call the first and simple thoughts of children, that come to them as, for example, they feel the pain caused when some gas enclosed in their intestines distends them, or the pleasure caused by the sweetness of the food that nourishes them . I call these direct and not reflexive thoughts; but when the young man feels something new and at the same time perceives that he has not felt the same thing before, I call this second perception a reflection, and I relate it only to the understanding, insofar as it is so attached to sensation that the two cannot be distinguished. Consciousness, in other words, presents a much higher, and much harder-to-establish, standard than mere potentiality of life. Therefore, implicit recourse to the concept fails as a basis for replacing viability as the line dividing the permissibility of abortion from its prohibition. For a fetus to be conscious in a sense that would establish it as a fully actualized human life, according both to current neuroscientific standards and to the philosophical tradition from which the concept stems, it would have to be capable of self-perception as well as simple perception of stimuli. And as philosophers of many stripes since Descartes have argued, self-perception is a reflexive state involving a concept of self in contrast with that of others - concepts it would be hard to imagine being meaningful for a fetus, even if fetuses could be shown to have access to concepts in the first place. By turning to consciousness in an attempt to push Roe's line-in-the-sand back toward conception, in other words, abortion opponents would in effect be pushing it forward, toward the sort of self-differentiation that only occurs well after birth and the emergence of what the phenomenological tradition has called "world." More than 200 years ago the German philosopher Immanuel Kant argued, in his "Critique of Pure Reason" that, while science can tell us much about the world we live in, it can tell us nothing about the existence of God, the immortality of the soul, or the origin of human freedom; moreover, he demonstrated with exquisite precision that should it try to come to conclusions about these questions, it would necessarily fall into error. This is the same sort of error committed by the polemicist Sam Harris in his recent argument against the existence of free will. In his book he cites advances in the neurosciences showing, for example, that computers attached to sensors can "read" test subjects' decisions some 300 milliseconds before the subjects report being aware of them. While he draws grand conclusions from such experiments, regarding the non-existence of free will and how we should organize and think about law and ethics, most reasonable peoples' response will inevitably be similar to that of Diogenes the cynic who, when faced with Zeno of Elea's watertight proof of the impossibility of motion, simply got up and walked. Likewise, while neuroscience may or may not be able to tell us something about the development of fetal nociceptive capacity, it has nothing to say about the fundamental question of what counts as a full-fledged person deserving of the rights afforded by a society. Science can no more decide that question than it can determine the existence or non-existence of God. Indeed, I doubt that members of the Idaho State Legislature would approve of using scientific evidence of the nonexistence of God to write a law depriving citizens of the right to worship as they choose; in the same way, they should avoid turning to neuroscience for evidence concerning the limits of personhood. The brain sciences, like all branches of the natural sciences, are immeasurably useful tools for individuals and communities to deploy (one hopes) for the improvement of our understanding of the natural world and the betterment of society. The basic rights guaranteed by the Constitution, however, have nothing at all to do with the truths of science. They are, to use Karl Popper's terminology, nonfalsifiable, like religious beliefs or statements about the immortality of the soul; to use Thomas Jefferson's word, they are inalienable. Like the equality of its citizens, in other words, the basic liberties of Americans should not be dependent on the changing opinions of science. When science becomes the sole or even primary arbiter of such basic notions as personhood, it ceases to be mankind's most useful servant and threatens, instead, to become its dictator. Science does not and should not have the power to absolve individuals and communities of the responsibility to choose. This emphatically does not mean that science should be left out of such personal and political debates. The more we know about the world the better positioned we are to make the best possible choices. But when science is used to replace thinking instead of complement it; when we claim to see in its results the reduction of all the complexity that constitutes the emergence of a human life or the choices and responsibilities of the person it may develop into; we relinquish something that Kant showed more than 200 years ago was essential to the very idea of a human being: our freedom. William Egginton is Andrew W. Mellon Professor in the Humanities at the Johns Hopkins University. His most recent book is "In Defense of Religious Moderation."