A Proof of the Existence of the Soul

There are two schools of thought regarding the nature of consciousness. There’s physicalism, also referred to as materialism, according to which consciousness is solely a product of brain activity and what I shall refer to as the spirit hypothesis, which holds that consciousness is contained in a nonphysical vehicle, referred to as the spirit or soul.

While research in areas such as near‑death experiences, out‑of‑body experiences, mediumship, and reincarnation has provided evidence in support of the spirit hypothesis, such evidence has been largely ignored by the mainstream scientific community, or else attributed, whether justifiably or not, to fraud or incompetence on the part of the researchers or fraud or self-delusion on the part of the experiencers. The proof presented here, which uses a series of thought experiments, has the virtue of not relying on the empirical data of psi research and is thus not vulnerable to such criticism, nor does it require accepting any questionable assumptions of a theological nature, such as the existence of God. It is only necessary to assume that you, the reader, are a conscious being.

In what follows, I will show that physicalism is fundamentally flawed and thus establish the spirit hypothesis. I will do so by assuming for the sake of argument the hypothesis of physicalism and showing that it leads to a contradiction.

Now, let’s introduce the device we will be using for our thought experiments: a matter duplicator. It has two chambers of equal size, which, anticipating the procedure to follow, may each be visualized as having the dimensions of a telephone booth.

The matter duplicator operates as follows. The item to be duplicated is placed in one of the chambers, designated as Booth 1. Both chambers are hermetically sealed. When the device is activated, any material initially in Booth 2, including the air, is annihilated; the contents of Booth 1 are scanned; and an exact atom‑for‑atom duplicate of the contents of Booth 1 is created in Booth 2. The duplication is assumed to occur within a time interval sufficiently short so that no significant change occurs to the contents of either booth during the duplication process, except, of course, the change in Booth 2 due to the duplication itself.

Now, suppose that you enter Booth 1, the matter duplicator is activated, and a duplicate of your body is created in Booth 2. In which body would your consciousness now reside? In the body in Booth 1, of course, since creating a duplicate of your body does not affect the original you, any more than taking your photograph captures your soul, notwithstanding the belief of certain primitive people to the contrary.

Let us now modify our matter duplicator so that immediately following the duplication operation previously described, the device swaps a designated subset of the contents of Booth 1 with the corresponding portion of the contents of Booth 2. We assume that the time required for the combined duplication and swap operations is sufficiently short so that no significant change occurs to the contents of either booth during that interval, other than the duplication and exchange.

Suppose, for example, that you enter Booth 1, and the device is set to exchange your right arm with that of your duplicate. After the duplication and swap, where would your consciousness be? In the body in Booth 1, since the duplication process does not affect the location of your consciousness and, since your consciousness does not reside in your arm, neither does the swap.

Now, suppose that your brain is switched with that of your duplicate. In which body would your consciousness now reside? According to physicalism, which we are now assuming, consciousness is a product of brain activity. In particular, your consciousness is a product of your brain’s activity. Thus, your consciousness would follow your brain into the body (sans brain) of your duplicate in Booth 2.

What if a single atom in your brain were exchanged with the corresponding atom in your duplicate’s brain? This would not affect the location of your consciousness because your body, including your brain, is continuously exchanging material with the environment without causing a loss of consciousness, and every atom in your brain eventually gets replaced.

Now, consider what would happen if a part of your brain of arbitrary size were swapped with the corresponding part of your duplicate’s brain. If the part of your brain that was exchanged were sufficiently small (for example, a single atom), your consciousness would remain in your original body. If the part of your brain that was exchanged were large enough (for example, your entire brain), your consciousness would be transferred to the body of your duplicate. Are there any other possibilities?

We cannot rule out the possibility that if a part of your brain of intermediate size were swapped with that of your duplicate’s brain, your consciousness could be annihilated. However, since the physicalist hypothesis rules out the existence of a disembodied consciousness, if your consciousness does exist following the swap, it must reside in one of the two bodies.

What about a partial transfer of consciousness? Suppose that as a result of the switch, some part of your consciousness ends up in the body of your duplicate. The host brain for that portion of your consciousness, although it consists partly of your original brain and partly of your duplicate’s brain, is nevertheless physically identical to your original brain and so, by the physicalist hypothesis, must have a consciousness identical to your original consciousness. In particular, all of your memories and mental faculties must be intact. Thus, if any portion of your consciousness is transferred to your duplicate’s body, your consciousness must be transferred in its entirety.

As a second argument against an incomplete transfer of consciousness, consider the situation as viewed by an external observer. Under the physicalist hypothesis, your body-brain-mind system can be viewed as merely a complex mechanism. Since the body of your duplicate, with or without a partial brain exchange with your original body, is physically identical to your original body, it must behave in the same way as your original body. In particular, its response to the question “Did you notice any change in your consciousness?” must be the same response that would be given by your original body, namely, “No.”

In summary, we have established that if any part of your brain is exchanged with the corresponding part of your duplicate’s brain, exactly one of the following must occur: (1) your consciousness remains with your original body, (2) your consciousness transfers to the body of your duplicate, or (3) your consciousness is annihilated.

Let n be the number of atoms in your brain at the time of the duplication/exchange, and let these atoms be numbered 1 through n in arbitrary order. Denote by A_i (A sub i) the subset of your brain consisting of atoms 1 through i. Since exchanging A_1 (that is, a single atom in your brain) with its counterpart in your duplicate’s brain results in your consciousness remaining in your original body, while switching A_n (that is, your entire brain) with its counterpart causes your consciousness to leave your body and enter your duplicate’s body, it follows that there is some number k between 1 and n–1 inclusive such that your consciousness remains in your body when A_k is exchanged with its counterpart but leaves your body, either to enter your duplicate’s body or to be annihilated, when A_{k+1} is exchanged with its counterpart.

Now, consider the effect of swapping A_k with its counterpart immediately followed by exchanging Atom k+1 with the corresponding atom in your duplicate’s brain. Since A_k and Atom k+1 together constitute A_{k+1}, the combined effect of these two exchanges is equivalent to switching A_{k+1} with its counterpart and must, therefore, result in your consciousness leaving your body. However, switching A_k with its counterpart is not in itself sufficient to cause your consciousness to leave your body, so the exiting of your consciousness must occur when Atom k+1 is exchanged with its corresponding atom. But, as argued previously, switching a single atom of your brain with the corresponding atom of your duplicate’s brain cannot result in your consciousness leaving your body. Thus, we have a contradiction, and so the physicalist hypothesis is disproved. Q.E.D.

We have thus shown that consciousness cannot be solely the result of brain function. While we have chosen to consider the brain as the purported seat of consciousness in the previous analysis because that is the view generally accepted by mainstream science, this proof could have been applied to any material structure purported to be the source of consciousness. Since consciousness cannot arise solely as the result of the activity of any physical entity, it must require the existence of a non-physical entity, which is customarily referred to as the spirit or soul.