The pro-life movement is often told that its struggles are a matter of tone, timing, or public relations. If only the message were softer, the messengers more likeable, the culture would come around. This diagnosis is mistaken. The real obstacle facing the pro-life position is not rhetorical but philosophical: the broader culture has adopted a worldview that differs from the pro-life position on two foundational questions, and no amount of marketing will resolve a disagreement that runs that deep.
The first question is what makes a human being valuable in the first place. Much of contemporary culture has embraced what might be called a performance view of human worth, in which dignity and a right to life are not grounded in what a being is, but in what it can do. On this view, value attaches to functions such as self-awareness, the ability to conceive of oneself as existing over time, or the capacity to form and act on desires. The competing view, historically grounded in the Christian understanding of the human person, holds that human beings are valuable in virtue of the kind of thing they are. As image-bearers, humans possess intrinsic purposes and intrinsic worth that do not depend on the exercise of any particular capacity.
The second disagreement concerns knowledge itself. The modernist inheritance of the Enlightenment holds that only empirically verifiable claims count as real knowledge, which leaves moral claims, unable to be measured or tested, in a permanently suspect category. Postmodernism goes further, denying that objective reality is even accessible, so that human nature, morality, and personal identity become matters of individual construction rather than discovery. Between a culture that doubts moral knowledge and a culture that doubts objective truth altogether, it is unsurprising that theories of personhood have emerged which sever a human being’s worth from human nature itself and relocate it in psychological performance. Philosopher Michael Tooley is one of the clearest articulators of such a theory, and his argument rewards careful examination, both for what it claims and for the pattern of reasoning it exemplifies.
Tooley’s Mental Continuity Theory
Tooley’s central claim is that an organism possesses a serious right to life only if it has a concept of itself as a continuing subject of experiences and mental states. Put plainly, what matters on this view is not an organism’s biological life but its biographical life: the presence of memories that link experiences together into a continuous psychological chain. Until that continuity exists, Tooley argues, there is no “self” present to possess rights.
This is a stronger and more unsettling claim than it might first appear. Tooley is not arguing merely that the unborn lack a right to life they will later acquire. He is arguing that no subject exists at all during the embryonic, fetal, or even newborn stages, because none of these stages involves the requisite continuity of memory. The unborn and the newborn are, on his account, potential rational agents rather than actual ones, and only actual rational agents possess desires and self-conception sufficient to ground a right to life. Species membership, on this view, does no moral work; a being can belong to the human species and still lack the psychological features that would make killing it wrong.
Tooley illustrates the argument with a now well-known thought experiment. Imagine a serum that, when injected into a kitten, transforms it from a potential rational agent into an actual one. Tooley asks whether anyone is obligated to administer the serum. Most people would say no. He then asks a follow-up question: if there is no obligation to begin the process of turning a potential rational agent into an actual one, what could be wrong with interrupting that process once it has begun? The thought experiment is designed to establish that there is no meaningful moral difference between withholding personhood and ending a process already underway toward it, and thus that acts such as abortion and infanticide are simply acceptable interruptions of an incomplete process.
Assessing the Argument
Several lines of response are available. The first concerns Tooley’s dismissal of species membership. Consider the difference between an accidental collision with a squirrel and one with a newborn, even a newborn with significant cognitive impairment. Almost no one treats these events as morally equivalent, and the reason is that human beings, by nature, belong to a kind that we treat differently from other kinds. The same intuition appears in judgments about flourishing: a dog that never learns to read is not experiencing a tragedy, but a teenager who cannot read is understood to be failing to flourish according to her nature. These asymmetries suggest that species membership is doing real moral work that Tooley’s theory cannot easily set aside.
A second problem concerns the grounding of rights in desires. If rights depend on an organism’s actual, exercised desires, troubling implications follow. A person born into slavery may not consciously desire freedom after prolonged subjugation; a suicidal person may not desire to continue living. Few would conclude that either is therefore not entitled to freedom or to life. Human beings are frequently entitled to goods they do not presently desire, which indicates that desire itself is not the relevant ground of entitlement.
A third and closely related issue is that Tooley’s theory rests on assertions rather than arguments. It is one thing to claim that memory continuity or the capacity for desire is what confers value; it is another to demonstrate why these particular traits, rather than others, are value-conferring. Pro-life advocates often unintentionally concede this point by responding with evidence that the unborn possess rudimentary versions of these traits, such as apparent responsiveness to a mother’s voice. Such responses implicitly accept that these traits are what matter, when the more fundamental task is to ask why any exercised psychological trait should be treated as value-giving in the first place.
The kitten serum thought experiment invites a further distinction between passive and active potential. A kitten becomes rational only through external intervention that changes its fundamental nature; it undergoes a substantial change from one kind of thing into another. The unborn human being requires no such external transformation. It is already rational by nature and needs only time and normal development to exercise that rationality. An embryo differs from an amoeba not merely in current capacity but in kind: the amoeba will never be rational because rationality is not part of its nature, while the embryo’s rationality is simply latent, awaiting maturation. Tooley’s argument therefore trades on an equivocation between two very different senses of potentiality.
The symmetry principle underlying Tooley’s kitten experiment can also be challenged directly. If one is asked to help carry a piano up a staircase and abandons the effort halfway, most people recognize an obligation was violated, even though there was no original obligation to begin. This suggests that beginning a process can generate responsibilities that did not exist beforehand, undermining Tooley’s claim that initiating and abandoning the development of a rational agent are morally equivalent to never initiating it at all.
The theory also struggles to account for human equality. If value derives from traits such as memory, self-awareness, or desire, and these traits vary enormously across individuals and across a single life, then equality itself becomes unstable. Abraham Lincoln confronted a structurally identical argument in defending the humanity of enslaved people. Lincoln did not claim that slaves were equal to their enslavers in intellect, business acumen, or political skill. He argued instead that equality rested on a shared human nature that did not depend on parity in exercised traits. The same reasoning applies to arguments grounding value in mental continuity: equality can be secured only by locating worth in a shared nature, not in unequally distributed capacities.
The Underlying Pattern
Beneath Tooley’s specific argument lies a broader pattern worth recognizing, since it recurs across many contemporary defenses of abortion. The first element of this pattern is body-self dualism, the assumption that the “real” person is constituted entirely by internal mental states, with the body serving as mere incidental matter. This assumption is difficult to sustain: harm to the body is experienced as harm to the person, and ordinary acts such as embracing a parent involve embracing a body, not an abstracted set of memories. A second element is the arbitrary selection of value-conferring traits, asserted rather than defended. A third element is the vulnerability of such theories to severe counterexamples. If only actual, self-aware persons possess rights, no principled objection remains to infanticide of healthy infants, organ harvesting from newborns, or non-consensual experimentation on the unborn, since none of these subjects yet possesses the psychological continuity the theory requires. Finally, these theories generate episodic paradoxes: a person who loses and later regains memory, as in a coma, would seem to become a different subject and then revert to the original one, an outcome that strains credulity.
Recognizing this pattern equips pro-life advocates to engage more effectively with theories like Tooley’s. Rather than accepting the premise that some exercised psychological trait determines worth, the more productive response is to ask why any such trait should be treated as decisive at all, and to locate human value instead in a shared human nature possessed equally by every member of the species, regardless of age, ability, or stage of development.