The public debate over whether unborn children feel pain has resurfaced, due to the recent passing of the “Pain-Capable Unborn Child Protection Act.”

Introduced by Rep. Trent Franks, R-Arizona, the legislation passed the House in early October by a 237-189 vote. The bill cites evidence that the unborn child can feel pain 20 weeks after fertilization, and therefore makes it a crime for anyone to execute an abortion at or past this age unless it is necessary to save the life of the mother or the pregnancy is the result of rape or incest.

What is this pain that unborn children feel?

Scientifically, the bill cites the presence of nociceptors, which are sensory receptors that respond to painful or injurious stimuli. This wiring, so to speak, is present throughout the entire body and linked to the growing brain very early in a child’s life. Even by eight weeks after fertilization, children respond to touch. By 20 weeks, when the wiring is complete, they react to stimuli by recoiling, and they experience a significant increase in stress hormones.

Such a physiological response is associated with long-term emotional and behavioral disabilities when fetuses are overly exposed to stressors during pregnancy. Hence, this measurable distress is defined as the pain that the unborn child feels.

This physical definition of pain — that nociceptors sense injury, notify the brain and cause a measurable and predicted response — is the most fundamental and quantitative tier. It is incontrovertible, observable, scientific fact.

Nevertheless, opponents call these claims “junk science” and “political myth.” While abortion advocates do not deny sensory or physiological responses as described in the bill, they believe that physical circuitry alone is not enough to feel pain.

According to a 2005 research review in the Journal of the American Medical Association, pain is “an emotional and psychological experience that requires conscious recognition of a noxious stimulus.” But how does one scientifically measure an emotional response in an unborn child?

The answer is, of course, you can’t. It is neither junk nor myth to insist that scientific conclusion be based on criteria that can be observed objectively.

In the fuzzier definitional tier of emotional interpretation, it is true that the child’s anatomy would require further development. The neurons that transmit signals to the brain must also reach to the cerebral cortex, the region that integrates information from multiple areas and plays a role in memory, perception, language and consciousness. The emotional and psychological reactions to pain also imply the presence of a mind.

The role of the cortex in awareness is not clear though. Children born with hydranencephaly (lacking a cerebral cortex) show the ability to interact with their environments. According to a 1999 paper in Developmental Medicine & Child Neurology, these children can recognize people and are social. Caregivers report that hydranencephalic children smile, giggle and cry. These actions suggest that a child’s mind is active even without a cerebral cortex.

Nevertheless, the American Congress of Obstetricians and Gynecologists (ACOG), representing more than 57,000 ob-gyns, issued a fact sheet in 2013 stating that a fetus does not have the physiological capacity to perceive pain emotionally and psychologically until at least 24 weeks of gestation.

Despite the subjectivity of the definition, the impossibility of making the measurement, and the lack of clarity about the role of a cerebral cortex, the medical doctors call this 24-week claim a fact. And abortion advocates nod in agreement. Strange, isn’t it?

Let’s be honest: Ultimately, it does not matter what anyone claims about fetal pain, except that the very claims themselves reveal something significant about each side’s motive. Abortion advocates summarily oppose any restrictions to abortion because to give an inch is to concede the humanity of the unborn. They will argue that pain begins later in pregnancy if that suffices. If the line is pushed, they will change the definition to fit their predetermined conclusion — because if it is ever not justifiable to kill an unwanted, unborn child, then it never is. Pain is simply the key word of the day.

I find it curious that the ACOG conceded that the unborn child can feel pain at 24 weeks when the body can both transmit signals from sensory nerves to the brain and process those signals. They could have gone further. The British Medical Journal published a 2006 paper in which the author concludes that “it is not possible for a fetus to experience pain” at all.

In this view, pain is not defined as a sensory response, nor is it defined as an emotional perception. Pain is defined as a subjective cognitive development that requires interactions with people and objects in the world (conveniently) outside the womb. The author, who served as an unpaid consultant for Planned Parenthood, compares the unborn child to fruit fly larvae that roll away from flames without cognition. Unless the unborn child can self-report the severity of his feelings on a pain scale, the child cannot be said to experience pain. But wait for it. If the Pain-Capable Unborn Child Protection Act passes in the Senate, the abortion logic likely will become further removed from objectivity.

Meanwhile, pro-life advocates remind the public that newborn children cannot explain what their pain feels like either. They point out that newborns are routinely assessed for pain based on observation of responses, such as facial expression, limb motion and squirming activity — the same kinds of physical indicators observed in 20-week-old unborn children.

Pro-life advocates remind them that unborn children, in fact, react so much to pain-inducing stimuli that doctors give them anesthesia before performing fetal surgery. Abortion advocates argue that the anesthesia is given to relax the mother’s uterus and immobilize the fetus during surgery so that the mother will not feel pain. They say it has nothing to do with the child’s comfort. But that is not true. The anesthesia also reduces the stress response in the unborn child so that the child will feel less pain after the surgery and heal faster.

The reasoning gets twisted here: If the child is going to live, then anesthesia should be provided for faster healing. If the child is going to die in abortion anyway, anesthesia obviously will not help the child heal. Make them say it.

Because if abortion advocates would stick to the simple fact that a human life begins at fertilization and that all humans have the right to life, then there would be no need for a “Pain-Capable Unborn Child Protection Act” in the first place. Since they are unwilling to adhere to strict science regarding the beginning of life, pro-life advocates must work to take smaller steps in the right direction by convincing the public of the humanity of the unborn child.

If it is by educating people about the pain an unborn child feels, so be it. We can appeal to emotion, too.

The pro-life logic is straightforward and sound. Whether a child has developed enough to feel pain or not, however pain is defined, the innocent child is still worthy of dignity, life and unconditional love. Period. This is not hard to grasp intellectually, and it ought to be a minimum requirement in a country that pledges liberty and justice for all.

Stacy A. Trasancos, Ph.D., is the author of Particles of Faith: A Catholic Guide to Navigating Science (Ave Maria Press).