Seven Proofs for the Natural Immortality of the Human Soul


The late Dr. Antony Flew—perhaps the greatest among atheist thinkers of the last 100 years—came to faith in God largely through his studies in philosophy and, most especially, science, as he recounted in his book written with Roy Abraham Varghese, “There is a God: How the World’s Most Notorious Atheist Changed His Mind.”

It was in 2004 that Dr. Flew rocked the world with his confession that he had come to believe in God. He made clear that he accepted deism, and not the God of the Bible, or of any other of the great world religions. But this in no way lessened the impact of his startling declaration. The reactions ranged from surprise, to disbelief, to even questioning whether Dr. Flew’s mental capacities were diminished, perhaps because of his age. He was 81 at the time of his “conversion.”

Let me assure you, as one who knows personally one of the men who walked alongside Dr. Flew on his journey toward truth, and who helped him to write the above-mentioned book, Roy Abraham Varghese, his radical change was very much real, his faculties were not diminished, and he was entirely free in his decision-making process.

It is interesting to note that in the second appendix of There is a God, there is a fascinating dialogue between Dr. Flew and New Testament scholar N.T. Wright on whether or not God has revealed himself to man, where Flew had this to say about Christianity:

I think that the Christian religion is the one religion that most clearly deserves to be honoured and respected whether or not its claim to be a divine revelation is true. There is nothing like the combination of a charismatic figure like Jesus and a first-class intellectual like St. Paul. … If you’re wanting Omnipotence to set up a religion, this is the one to beat (pp. 185–186).

Dr. Flew never came to accept Christ or Christianity, or any of the distinctively Christian teachings like the inspiration of Scripture, the Trinity, the divinity of Christ, the incarnation of Christ, etc. This is almost to be expected as they are dependent upon supernatural assistance and the acceptance of divine revelation. As a deist, Flew would have accepted none of these teachings.

But interestingly enough, Flew also never came to accept the immortality of the human soul. And this is a truth that is knowable by the natural light of reason apart from revelation. This makes me wonder if this may well have been the linchpin that, if understood and accepted, might have completed the foundation for Dr. Flew upon which the entirety of the revelation of God may well have been able to rest. Perhaps then Dr. Flew would have been able to accept the further light of revelation?


Because Dr. Flew, unfortunately, died in 2010, just six years after his declaration of faith, I also wonder if time simply ran out before he would have come to the fullness of truth. This we will not know this side of eternity. But I do think we can rejoice in a reasonable hope that he was heading in the right direction when he passed away. Dr. Flew was truly a fascinating man. And, according to my friend Roy Abraham Varghese, he was a good man as well.

Our Reason Tells Us So

Dr. Flew was certainly not alone in his struggle with the concept of the natural immortality of the human soul. (I say “natural” because human beings uniquely possess an immortal soul by nature. That means, man does not need grace in order for his soul to live forever. It would do so naturally, even if he ends up in the isolation and emptiness of hell forever.) This is a point of difficulty for many skepetics. Thus, it is crucial for Christians to know how to explain it to skeptics. And to know that we don’t need a Bible to be able to do so.

The Bible certainly more than helps those who believe in its inspiration, and in the Church that has the authority to definitively interpret it. Through these great gifts, all can know the essential truths of the Faith, including the natural immortality of the human soul, both easily and infallibly. But this hardly helps when you are speaking to someone who doesn’t accept the Bible as God’s word.

The truth is, we can can demonstrate this truth through reason alone, i.e., through philosophy. But first we need to establish the fact that humans have souls at all, and define our terms.

Does Fido Have a Soul?

The soul is, by definition, the unifying and vivifying principle that accounts for the life and what philosophers call the “immanent action” of all living things. The word “immanent” comes from two Latin words that mean “to remain” and “in.” “Immanent action” means the multiple parts that comprise a living being are able to act “from within” in a unified way, and in accordance with its given nature, for the good of the whole being. The soul is what accounts for this unified action that is essential for there to be life.

This comes as a surprise to many Christians with whom I speak, but St. Thomas Aquinas tells us, and it follows from our definition of the soul above, that not only humans, but non-rational animals and plants have souls as well. Man alone possesses what St. Thomas calls a “rational,” or “spiritual” soul. Plants and animals possess “material souls” that, unlike human souls, are dependent upon matter for their existence. But they possess souls nonetheless.

To be precise, there are three categories of souls:

1. Vegetative – This category of soul empowers its host to be able to take in nutrition and hydration, grow, and reproduce others of its kind. A rock can’t do this!

2. Sensitive – An animal with a sensitive soul can also acquire sense knowledge and use locomotion to both ward off danger and to gather goods it needs to survive and thrive.

These first two categories of souls are material in nature. By that I mean, they are entirely dependent upon the material body for their existence. As St. Thomas says, “They are adduced from the potency of the matter.” When the host dies, the vegetative or sensitive soul ceases to exist.

3. Rational – Capable of all the above, the animal possessing a rational soul is capable of acquiring intellectual, or “spiritual,” knowledge as well, and of choosing to freely act toward chosen ends.

The question now becomes: how does any of this demonstrate the soul of man to be immortal?

What is Death?

In order to get where we need to go, we first have to define death. CCC 997 defines it as, “… the separation of the soul from the body”—an excellent definition. But perhaps a more precise philosophical definition is: “The reduction of a composite being into its component parts.” This is why I would say when Fido dies, you might want to get him out of the house and bury him. It won’t take long for him to start the process to becoming “reduced to his component parts.” And that process gets a bit messy!

However, a spirit, by definition, has no parts. There is nothing to be “reduced to its component parts.” Thus, that which is purely spiritual cannot die.

So for my first four proofs for the immortality of the soul, I am going to demonstrate it by showing the soul to be “spiritual” in nature. If I can do this, I will have accomplished the task at hand.

For my fifth, sixth, and seventh proofs, I will make my appeal through what we find in human experience down through the millennia that points us in the direction of man possessing an immortal soul.

The Soul, the Person, and the Body

The two principle powers of the soul are its power to know and to will. Why do we say these powers lie in the soul? In simple terms, it is because it is the entire man that comes to “know” or to “love” (love being the highest purpose of the will) not just “part” of him. This would seem to indicate that the same “unifying and vivifying principle” that explains man’s life, would also explain his power to know and to will.

But man is more than just a soul. He also directly experiences the “I” that unifies all that he is and all that he has done down through the decades of his life. This “I” represents the individual “person” that constitutes each human being.

Is there a distinction between the soul and the person? Yes. But it can be a bit tricky to demonstrate.

Perhaps it would best to demonstrate the distinctions by laying out some of the differences between the body, soul, and person.

There is no doubt that the body contributes to the soul’s ability to come to know. A damaged brain is a clear indicator here. The soul needs a properly functioning brain to be able to come to know anything, ordinarily speaking.

Yet, it is also interesting to note that according to philosopher and theologian, J.P. Moreland, man is much more than a body as well. Moreland provides:

“… neurosurgeon Wilder Penfield electrically stimulated the brains of epilepsy patients and found he could cause them to move their arms or legs, turn their heads or eyes, talk or swallow…”

But yet, Moreland says, the “patient would respond by saying, ‘I didn’t do that. You did.”’ Further, no matter how much probing and electrical prodding, Penfield found there is no place in the brain that can “cause a patient to believe or decide” (Lee Strobel, The Case for a Creator, p. 258.).

Thus, the “I,” or, the person, seems to use his body, or here, his brain, to be sure, but “he” is not determined by it.

We can also say with confidence that the “I” is not synonymous with the intellect and will, or the soul, either because “I” can struggle to remember, to know, or to exercise its will. There seems to be more to a person than just a body, or even just a soul. Man seems to be a body/soul composite. Both his body and soul contribute to the great and mysterious “I.”

The Seven Proofs for the Natural Immortality of the Human Soul

1. The Intellect Possesses the Power of Abstraction

St. Thomas Aquinas explained, “The operation of anything follows the mode of its being” (Summa Theologica, Pt. 1, Q. 75, art. 3). To put it in simpler terms: action follows being. One can tell something of the nature of a thing through examining its actions. Hence, the spiritual nature of the human soul; and therefore its immortality, can be proven through the exhibition of its spiritual power in human acts. One such “spiritual action” is the power of abstraction.

To use thomistic language once again, when a human being comes to know something or someone, let’s say, he sees a man, “Tim,” his senses engage the individual; “Tim,” through the immediate “accidental” qualities that he sees. By “accidentals,” we mean the non-essential, or changeable, aspects of “Tim” like his size, color, or colors, weight, etc. From this conglomeration of accidentals, his intellect abstracts the “form” of “man-ness” from that individual (This reminds me of a philosophy professor I had in college who seemed to have an inability to pronounce a noun without adding a “ness” to the end of it.).

This “form” the intellect abstracts is an immaterial likeness of the object thought about or seen. It is ordinarily derived from a particular object, like the man, “Tim,” as I mentioned above, but it transcends the particular individual. The form gets at the essence of “Tim.” It is that which is universal concerning “Tim,” the man. He is risible (he laughs), he reasons, he worships, and more. This is that which is changeless and applies not just to “Tim,” but to all men. And very importantly for our purpose, we must remember that this essential “form” abstracted by the intellect is a spiritual reality. It transcends the individual.

Now, there is a material likeness, or image, that is concrete and singular, impressed in the memory of man, but that is not what we are talking about here. Dogs, cats, birds, and bats have memory. Non-rational animals do not have the power to abstract the form of “man.” Only human beings can comprehend “man-ness” or “dog-ness.”

This is not to say the soul of a dog is not real. It is, as St. Thomas Aquinas says, a “real principle,” and it is “adduced from the potency of the matter.” This is analogous to elements formed into a compound or an atomic explosion caused from the potency of the matter used in the formation of a bomb. Certain kinds of matter exist in potency to other kinds of matter that when joined create elements, atomic explosions, or Fido! But only man (among animals on earth) has this power of abstraction that necessarily involves a spiritual principle.

Why is this crucial to understand? Well, let’s introduce yet another “form” here… “tree-ness.” “Tree” is defined as, “A woody perennial plant, having a single main stem or trunk arising from the soil and having branches and foliage.” This would represent “the form” that is common to all trees apart from any particular. I could burn the individual tree from which I abstract the form of “tree-ness,” and reduce it to ash so that there is no longer this particular “tree” in existence, but I can never burn “tree-ness” because it is “spiritual,” or “universal.”

Remember our philosophical principle? “Action follows being?” If the soul has this spiritual power to “abstract” the form of “tree,” or “man,” it must be spiritual. And if the soul is spiritual, it has to be immortal. It cannot be “reduced to its component parts.”

2. The Soul Forms Ideas of Realities That Are Immaterial

The human soul not only abstracts the forms of material entities encountered, but it also has the power to know the ideas or “forms” of immaterial realities like logical sequence, moral goodness, property rights, philosophical categories like “substance,” cause and effect, and more.

Where are these realities? What color are they? How big are they? How much do they weigh?

They have no color, size, or weight because they are spiritual—and by definition—immaterial. Sense image alone (like the Empiricists John Locke and David Hume say is the only source of knowledge) cannot account for these. We are not talking about the material world here.

To form an idea of something spiritual, again, requires a spiritual principle, i.e., the soul. If it’s spiritual, it can’t die.

3. The Will Strives for Immaterial Goods

Closely related to my first two proofs, just as the intellect has the power to abstract the “spiritual” forms of the things and beings it encounters, and to form ideas of immaterial realities, the will also has the power to strive for immaterial things, like prudence, justice, temperance, fortitude, etc. One cannot produce what one does not possess. There must be a spiritual; and therefore, immortal principle (the soul), to will these spiritual realities.

4. The Intellect Can Reflect Upon Its Own Act of Knowledge

It could not do so if it were material. A material faculty, such as the power of vision, only reacts in response to external stimuli. It could only be said to “perceive” inasmuch as one “part” was acted upon by another “part” of something else. When our intellect reflects on its own act of knowing, and we could add its own act of being as well, it is both subject and object of knowledge. The soul can only do this if it has no parts. A dog cannot reflect on its own act of knowing, or being. It just scratches! That is sense knowledge.

5. Man Has a Natural Desire to Live Forever

Aristotle gave us an extremely important philosophical principle when he said, “A potency without the possibility of actuality destroys nature.”

The existence of acorns necessitate the existence of oak trees. It is not that each individual acorn will be actualized and become an oak tree. That is clearly not the case. But if no acorns could be actualized, there would be no oak trees.

We could multiply examples here. A digestive system in animals necessarily means we can know there is food… somewhere out there. A female dog necessitates the existence of a male dog. If there’s not, then “dog” will be eliminated in fairly short order.

Thus, the non-rational animal seeks self-preservation, food and sex. Each of these is conditioned by time. Man has intellectual knowledge which is absolute. The “forms” are not conditioned to time as material knowledge is. Remember? The individual “tree” will die, but not the “form” or “idea” of tree that man alone possesses among creatures of earth. From this knowledge of the eternal springs a spontaneous desire to live forever. And this potency cannot exist in vain. That would be contrary to everything we see in nature.

6. The Testimony of Mankind Over the Centuries and Millennia

From ancient Egypt’s Book of the Dead, to Western Civilization’s Bible, every civilization, every culture, in all of human history has attested to the existence of an after-life.

Some will point out the very few exceptions—one being Hinayana (or Theravedic) Buddhism—that deny the existence of “spirit,” or the soul, to discount this our sixth proof. But to no avail.

Actually, the exception tends to prove the rule. And this, I would argue, is certainly the case with Hinayana Buddhism. Not only is this ancient form of Buddhism an anomaly in the world of religion, but the appearance of Mahayana Buddhism (that restored belief in “God” and “the soul”), very early in the history of Buddhism, and the fact that it is today by far the largest of the three main traditions of Buddhism, tends to demonstrate that man is so ordered to believe in the afterlife that errant thinking here or there over millenia can never keep its truth suppressed for very long.

7. The Existence of the Moral Law

My final proof for the natural immortality of the human soul is derived from the existence of the Moral Law that we can know apart from divine revelation. This is a true law knowable to all, and a law that man did not give to himself. And yet, it is often unpunished and the sanctions of law not carried out. Hence, there must be an eternity where all is rectified.

Necessarily rooted in the reality of the justice and wisdom of God who created both us and this that we call “Natural Law,” Plato said without the immortality of the soul there is no justice, which would be absurd. If there is a God who is just, then there must be final justice. Since final justice so often does not occur in this life, there must be a next life in which justice will be served.

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