Many contributors to Public Discourse, including myself, come from the field of philosophy. This shapes what and how we write, both for Public Discourse and in our other work. Yet our work overlaps in important ways with work in other disciplines. In particular, those of us who write about the embryo and embryo ethics rely upon work in embryology and developmental biology. We could plausibly call at least some of the results of our work philosophical embryology, but this raises important questions about what we are doing. In particular, how does—or, better, how should—philosophy relate to non-philosophical fields, and, further, when does philosophical embryology become something else, such as philosophical ethics or politics?

Embryology and developmental biology are familiar fields of the life sciences. Scientists study the development of various organisms, seeking to understand the mechanisms by which organisms will change from one state of development to another, the conditions that will prevent such developments, and whether those conditions be internal, such as a gene mutation, or external, such as an environmental factor. These scientists study the conditions that bring about the transition from something that was not a new organism (a gametic cell, for example) to something that is a new organism (a zygote, for example). More recently, as part of the so-called evo-devo program of research, scientists study both embryonic development and evolution in light of one another.

What does philosophy add to this picture? Philosophical embryology is a branch of theoretical philosophy. So it does not, in itself, seek to answer any practical questions about the appropriate treatment of embryos, human or otherwise. Indeed, to be reasonably pursued, philosophical embryology must rigorously refrain from using moral or practical considerations to answer questions appropriate to its domain. Some thinkers, however, such as Ronald Green and Jane Maienschein, have suggested that theoretical questions about embryos require choices, and choices must be guided by practical values and desired states of affairs. This strikes me as inappropriate, and I’ll explain why shortly. But first I need to identify some general characteristics of philosophy, especially theoretical philosophy.

First, philosophy operates at a level of generality greater than that appropriate to the empirical sciences. St. Thomas’ introduction to his commentary on Aristotle’s Nicomachean Ethics is a good example of this. Aquinas identifies four “orders” that he thinks roughly divide up the ontological terrain that human beings inhabit: the order of nature, which exists independently of us, the logical order introduced into human intellection by thought, the practical order introduced into our actions through intelligent deliberation and choice, and the order of making introduced into the material of the world by our work. This fourfold categorization is extremely broad. In each category of order, more specific but still quite abstract categories can be discussed profitably by philosophers, such as those of substance and accident, subject and predicate, act and intention, or of purpose and function.

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Second, philosophy involves the sorts of questions that, as Thomas Nagel puts it, “the reflective human mind finds naturally puzzling.” Such questions attempt to get beyond what is given in experience, to find the what-is-it of something, the why-is-it of something, or to find the relationship between apparently dissimilar realities. Some such questions, of course, do not require philosophical answers; the empirical sciences can identify certain realities (“that is a liver cell”), or explain how they got to be as they are (“a particular set of signals induced a particular set of changes”), or identify the relationship between two otherwise similar or dissimilar entities (“this cell’s division gave rise to that cell,” or “this earlier healthy cell is identical to that later diseased cell”).

But other questions, and sometimes the very same questions prosecuted to a further degree, require answers that take on the shades of generality just discussed. For example, philosophers will query what it means to say that something is a biological substance, or that one biological state of affairs causes, but is not identical to, another, or what it means to say that biologists know what they claim to know. And here, it is worth noting, at least at certain initial stages of inquiry, the concepts used in philosophy will overlap, perhaps considerably, with the concepts used in science. Thus, the question, “what is that,” and the answer, “it is a living organism of such and such a species,” will raise philosophical questions: “What is an organism? What is it for something to be alive? What is a species?”

What level of generality or reflectiveness is sufficient for a question or its answer to be philosophical? Answers to this will be contestable, and a familiar dialectic of objection, defense, distinction, and argument will ensue as regards the boundaries between philosophy and the disciplines it abuts. However, although there are disagreements here, it is important to get the boundaries correct: When a question can be answered by science, it should be; and philosophy should take that answer as its datum. Likewise, when a question cannot be answered by science, it should be recognized that the attempted answer belongs to a different discipline such as philosophy. And some questions, perhaps, should be seen as inevitably mixed in character.

The importance of this point can be illustrated in the following way. Pointing to a broad swath of embryological and developmental biology textbooks, writers such as Patrick Lee, Robert P. George, and myself have claimed that there is a general consensus among biologists as to when the life of an individual human being begins, viz., at fertilization, unless the individual is a monozygotic twin, or a product of human cloning. Yet, in a recent essay, the eminent biologist F. Scott Gilbert attempts to refute the “error” that there is a consensus among scientists “as to when life begins.” Gilbert identifies five different views, ranging from fertilization up to birth.

But it is worth noting some important features of Gilbert’s refutation of the alleged consensus. Many of the sources he cites for views other than fertilization are not scientists, but rather are philosophers, political theorists, or theologians. More importantly, Gilbert shifts very quickly from speaking of a consensus on when an individual human life begins to speaking of the onset of “personhood.” And this is surely a failure to respect disciplinary boundaries. “Personhood,” while potentially an important philosophical concept for the discussion of the embryo, is no biological concept at all. So no attempt to answer the biological question, “when does the life of an individual human being begin,” should be answered by reference to the concept of “personhood.”

It is further worth noting that even when Gilbert does quote scientists it is often in a context that makes clear that they too are making this mistake. Thus embryologist Marilyn Renfree is quoted as saying “Assuming that monozygotic twins have separate souls, it follows that ensoulment must occur after cleavage.” Here “soul” is a stand-in for “person” and is every bit as non-biological a concept. Maienschein denies that there is scientific consensus about when there is the beginning of a “meaningful” life. But scientists should not, qua scientists, be expected to reach consensus on what counts as “meaningful.” Philosophers, as a result, in orienting their inquiries into the embryo, should begin by identifying what biologists say about the embryo insofar as they are speaking from a biological standpoint.

Still, as mentioned these philosophical claims about the appropriate boundaries of philosophy will not go uncontested. Neither, once boundary questions are settled, will the substantive questions of philosophy will themselves be accepted without objection. So a third general characteristic of philosophy is, in fact, the inevitability of argument. And reflection on this feature leads to a fourth characteristic of philosophy, perhaps the one considered most important by its early practitioners, namely that it is pursued out of a love of truth. The dialectic of philosophy shorn of this motive is, in fact, the dialectic of sophistry, a description concerned as much or more with a moral failing at the root of one’s vocational commitment to philosophy as with a failure to successfully prosecute that vocation.

Now, philosophical embryology abuts the scientific disciplines of embryology and developmental biology. It must therefore have three concerns: First, a concern to describe the realities discovered by embryology and developmental biology at a higher level of generality than is achieved by those disciplines, with a view to integrating this more general representation of the realities studied by these disciplines with philosophy’s own more general concepts and representations (e.g., philosophical embryology will attempt to integrate the discussion of organism with that of substance). Second, it must be concerned to answer those reflective philosophical questions raised by the study of embryological development if, as I believe, there are any (what is it, for example, for an organism to exist as a whole, as a “this something,” as a substance?). And third, it must be prepared to engage in a philosophical dialectic with those whose general representations work with a different set of concepts, or who answer philosophical questions differently, or who dispute the boundaries between the scientific and the philosophical, whether on some local matter, or more globally (e.g., those who think “personhood” is the initial ontological point of departure for philosophical embryology).

Through it all philosophers interested in the philosophical questions of embryology must be concerned for the truth as such, no small feat when matters of great practical weight can turn on the results of embryological and philosophical investigation. But this is why it seems so inappropriate to frame the initial philosophical, and even scientific, questions in terms of our values, interests, or pragmatic concerns, as do Green and Maienschein. To do so abandons both philosophy and science in this area by presupposing that there really are no answers to the questions of interest, just interests in particular answers.

Of course, this is not to say that our interest—that of the authors for Public Discourse, its readers, and others engaged in philosophical embryology around the world—is disengaged from practical concerns. Far from it. For the very concerns that are raised theoretically in philosophical embryology—“What is an embryo? When does an embryo come to exist? What does the phenomenon of twinning imply about the individuality of the embryo?”— have clear bearing on practical issues of tremendous personal and social importance: “Is the cloning and destroying of embryos permissible? Is destructive research on spare embryos from in vitro fertilization permissible? Is abortion morally or politically choiceworthy?” These questions are insistent, and, tied up as they are with questions of justice, they make a moral demand on every person of good will to answer them as best they can.

My point, then, is not to deny these overarching practical concerns. But, insofar as those of us who are concerned to defend the embryo draw on philosophy, or seek to engage philosophically with the issue, then we and our opponents must attend to these four imperatives: First and foremost, be concerned for the truth. Second, engage in our dialectical engagements and arguments with a view to seeking and defending that truth. Third, be alert to the questions a reflective mind would acknowledge as puzzling and attempt answers to them, rather than putting them aside as threatening. And fourth, respect the boundaries between the generality of philosophy and the empirical detail of the science, on the one hand, and between theoretical and practical investigation on the other. Consensus in philosophy is rare but possible; and, in this area, it is a necessary step towards resolution of important moral and political issues. It is only by being true to what philosophy is, however, that such a meaningful resolution will come about.