Scientists are often not fond of the idea of metaphysics. Physics is, of course, the study of the natural world and universe. Metaphysics is the study of what is really real. It implies that there is something beyond physics and, therefore, beyond the natural world and the physical universe. This is anathema to scientism—that is, scientific naturalism: how dare one assume that there exists something beyond nature, especially since there is no physical and testable evidence of such things?

Yet there seems to be a prominent and curious case of when metaphysics is appealed to when science disagrees with what people want to believe...

For many people, metaphysics is not so controversial. Metaphysics can consider questions such as whether God exists, where He resides, His nature, etc. It also ponders what beauty (aesthetics) is, what ethics and morality are and where they come from, and more. Metaphysics, therefore, is a window into examining aspects of reality which many believe science cannot answer. Because metaphysics deals with questions about the spiritual, the abstract, and what has eluded science until now (and possibly always will), it is confined to the realm of philosophy (and divine revelation).

The rejection of metaphysics is part of an effort to ditch philosophy in favour of (natural) science; the thought being that science is able to, and eventually will be able to, answer all questions about reality. What science cannot answer, is not real, and therefore is not worth any time to be considered; or so the thinking goes.

During the Enlightenment, it seemed like science and philosophy would both lead to the downfall of religion. As theistic philosophers turned the tables somewhat, anti-theists were left with only science to wage their crusade of naturalism.

But sometimes scientific fact is inconvenient. And when this is the case, it is convenient to appeal to metaphysics to carry their arguments further.

The specific example which I have in mind, is that of the question of personhood. Those who have pro-choice/pro-abortion arguments have the following dilemma:

1. It is unethical to kill an innocent human being.
2. Science has determined that a new human organism is formed at the moment of conception.
3. Therefore, terminating pregnancy should be unethical.

The claim that new life is formed at conception should really not be a controversial statement at all. Unlike sperm and egg cells, a zygote has distinct DNA from the parents (therefore, the zygote is not a part, as hair and skin are, but a whole of a new organism). The cells of a healthy zygote are also distinct from cells in post-birth humans, because they will continue to divide and develop naturally into distinct, more specialised cells, taking the human organism to its next stage of development (although post-birth humans will also continue through further developmental cycles, such as puberty, and menopause in females). It is therefore different from, say, a human in a vegetative mental state, because it is a natural part of the development of any human being, while being in a vegetative state does not lead to a new developmental phase, and does not benefit the person.

Raising this point is irksome to the person trying to defend a pro-choice stance. A common response is to then raise the objection that a zygote or embryo is not a human person. Ethics, morality, and the rule of law apply to persons, whereas non-person human organisms do not need to be afforded such considerations.

This kind of reasoning has always been perplexing to me, particularly if the person making such an argument otherwise holds to scientific naturalism. The question of personhood (if it even exists) falls within the realm of metaphysics. Physics has spoken: a zygote is a new, distinct human organism.

It is not my intention to explore whether the question of personhood has any merit in any great detail. My only intention is to show the tension which can exist when this argument is made. A person discussing this topic should be aware of it, and call out any double standards being employed by the person making the arguments. The purpose is of course not to win arguments, but to hopefully force people to reconsider their positions by making sound, rational arguments (in a kind and loving way). The purpose is not to be right: it is to save the lives of innocent humans who cannot yet speak for themselves.

Calling this out will, of course, only help if the other person in the discussion is a scientific naturalist. As mentioned at earlier in this article, not everyone (or even most people) is. The question of personhood opens a whole other can of worms: is personhood achieved after the first or second trimesters? If so, why? Is it achieved when the "quickening" happens? If so, what happens if the mother misses this event (such as during sleep)? And why does foetal motion equate sentience? Or is personhood achieved once a baby or toddler starts showing self-awareness (as Peter Singer argues)? If so, can we always be sure the child will immediately demonstrate outwardly how they have developed inwardly? Or can parents necessarily accurately judge when a child has become self-aware?

These are handful of considerations which needs to be worked through if one rejects the scientific reality that a new and distinct life is formed at the moment of conception, and that the new life should be treated as a human being.