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How Do You Know You Are Not the Only Human Who Ever Existed?

Can evidence or logic help you decide? You might be surprised…

Solipsism is the belief that you are the only human being who has ever existed; all others are the inventions of your imagination.

G.K. Chesterton famously received a letter from a reader who commented (I paraphrase), ‘Solipsism is a compelling metaphysical position. I’m surprised more people don’t believe it.”

At Scientific American, columnist John Horgan describes solipsism as a central dilemma of human life. In a recent essay, “How do I know I’m not the only conscious being in the universe?”, he writes,

It is a central dilemma of human life—more urgent, arguably, than the inevitability of suffering and death. I have been brooding and ranting to my students about it for years. It surely troubles us more than ever during this plague-ridden era. Philosophers call it the problem of other minds. I prefer to call it the solipsism problem.

John Horgan, “How Do I Know I’m Not the Only Conscious Being in the Universe?” at Scientific American

Horgan explains,

Solipsism, technically, is an extreme form of skepticism, at once utterly nuts and irrefutable. It holds that you are the only conscious being in existence. The cosmos sprang into existence when you became sentient, and it will vanish when you die. As crazy as this proposition seems, it rests on a brute fact: each of us is sealed in an impermeable prison cell of subjective awareness. Even our most intimate exchanges might as well be carried out via Zoom… You experience your own mind every waking second, but you can only infer the existence of other minds through indirect means.

John Horgan, “How Do I Know I’m Not the Only Conscious Being in the Universe?” at Scientific American

Horgan rambles on, offering mostly pop psychology and a dash of evolutionary psychology. Looking beyond the shallowness of his discussion, extreme skepticism—of which solipsism is an iteration—does raise profound issues. In particular, we must consider how it affects the foundations of atheism and of belief in God.

What do we know with certainty? The surprising answer is nothing. If we experience a sensation, it is possible that that sensation is merely a trick or our mind. Concepts that seem obviously true may be delusions. There is nothing we can be sure of. Nothing.

Now, many readers will say, as did René Descartes, “I am absolutely sure of this: I think, therefore I am.” But can you even be absolutely sure of your own existence? Before you say “That’s crazy,” let me explain.

“I think therefore I am” is not the most fundamental claim we can make about the nature of knowledge (an epistemological claim). Why not? “I think therefore I am” depends critically on “therefore”—that is, it depends on logic, specifically on the law of non-contradiction.

The law of non-contradiction says that two contradictory positions cannot both be true in the same way at the same time. I cannot exist (in order to assert my existence) and simultaneously not exist. And of course we all accept that law. But notice—we believe in the law of non-contradiction; we don’t know it. And we can’t logically claim that we absolutely know it, because any claim to the truth of the law of non-contradiction depends on… the law of non-contradiction. To claim that the law of non-contradiction is certain is to reason in a circle.

But note what follows: Because we can’t prove that logic is true, we could “think” but not “exist”! Thus we can’t even claim to know with certainty that we exist. To do so is to invoke a law of logic that, however obvious it seems, we must take on faith.

Our most fundamental knowledge is of logic—specifically, the law of non-contradiction—and even that we must take on faith.

So we are all genuinely in a position of radical skepticism—we have absolutely certain knowledge of nothing, not even of the laws of logic, not even of the certainty of our own existence.

But of course, we all believe that logic is true, that we exist, that solipsism is not true, etc. These are reasonable beliefs and life would be difficult if we didn’t believe them. But they are beliefs, not certain knowledge.

Now an astute reader may object that I contradict myself—I am claiming absolute knowledge that… there is no absolute knowledge! That’s correct—and therein lies the problem. No knowledge of any sort can be grounded in certainty—not even knowledge that no knowledge of any sort can be grounded in certainty! The uncertainty of knowledge is radical. Thus, the “certainty of human knowledge” is nonsense, and the certainty of that statement itself is nonsense, and…

And yet… we all have faith that our knowledge is true—faith in our knowledge of logic, faith in our existence, and faith in countless other reasonable things. But it is faith—we have no certain knowledge whatsoever. That is the human condition.

But atheists and those of us who believe in God have very different kinds of faith in logic, reason, existence, etc. Atheists must take everything on faith. Their faith is incoherent, in the sense that atheist faith is brute belief, without a rational framework.

Believers in God—the God of Christian and Jewish theology Who is omniscient and Who is the Source of all truth and reason—have a coherent epistemology. We still need faith—everyone needs faith—but our faith is in the Source of all logic and truth, so the laws of logic and the certainty of existence and of moral law are rational consequences of our fundamental faith in God.

All human knowledge is faith. Atheism is incoherent faith—the belief that logic and existence are mere brute facts. Belief in God is coherent faith—the belief in a Creator who is the Source of logic and existence.

To sum up, the solipsists do have a point. Radical skepticism is part of the human condition. We all need faith. Belief in God, unlike atheist belief, provides a coherent framework on which to understand reality.

You may also enjoy:

Physicist rejects free will — and thus fails logic. If we accepted his argument for materialism, we would have to stop believing in it—a curious, self-refuting result.


Interview with a woman (or women) formerly called Susan Blackmore. A professor of psychology argues that there is no continuity between our present selves and our past selves.

Michael Egnor

Senior Fellow, Center for Natural & Artificial Intelligence
Michael R. Egnor, MD, is a Professor of Neurosurgery and Pediatrics at State University of New York, Stony Brook, has served as the Director of Pediatric Neurosurgery, and award-winning brain surgeon. He was named one of New York’s best doctors by the New York Magazine in 2005. He received his medical education at Columbia University College of Physicians and Surgeons and completed his residency at Jackson Memorial Hospital. His research on hydrocephalus has been published in journals including Journal of Neurosurgery, Pediatrics, and Cerebrospinal Fluid Research. He is on the Scientific Advisory Board of the Hydrocephalus Association in the United States and has lectured extensively throughout the United States and Europe.

How Do You Know You Are Not the Only Human Who Ever Existed?