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How to refute skepticism

Romans 1:18-32 explains that God’s creation proclaims His existence, as well as our guilt, such that everyone is left “without excuse.”

 Yet rebellious man wants some sort of excuse. So one that he offers is that our sense can be fooled, and our thinking too, so – these extreme skeptics propose – can we really know anything at all? And if we can’t know anything, how can we be held accountable? But, as John Byl explains in this excerpt from his book “The Divine Challenge,” such skepticism is self-defeating.


Skepticism about human ability to acquire knowledge is as old as philosophy. The Greek philosopher Pyrrho (circa 360-270 BC), who had been in the army of Alexander the Great, taught skepticism regarding the senses, logic, and morals. He affirmed that there were no rational grounds for preferring one belief above another. Hence one should renounce all claims to knowledge.

A somewhat more recent advocate of skepticism was the philosopher David Hume (1711-1776). Hume believed that all our knowledge derives from sense impressions. Consequently, he denied the validity of all abstract ideas, including notions of causation, the external world, and even the self.

Skepticism is appealing to the intellectually lazy for, if all knowledge is reduced to the status of mere opinion, the ignorant is as wise as the learned scholar. 

1. Test the assumptions

How would one refute skepticism?

Any worldview consists of various presuppositions, accepted on faith, and their logical consequences. One might start, therefore, by analyzing, one by one, each of the skeptic’s premises as to its plausibility.

Take, for example, Hume’s assumption that our minds consist entirely of a succession of perceptions, without any trace of intellectuality. This presupposition alone already leaves no room for any thinking about our perceptions or how they are linked. Once one adopts a more comprehensive view of mind, Hume’s skeptical conclusions no longer follow.

Often, however, the initial errors are small and not easily discerned. It is only later, after a long train of thought, that they produce significant consequences. As Aristotle noted in De Caelo (On the Heavens),

The least initial deviation from the truth is multiplied later a thousand-fold…that which was small at the start turns out a giant at the end. (1)

2. Try out the system

This suggests a second, more indirect approach. Instead of examining presuppositions individually, we can examine them together, as a unit. One way we can test the plausibility of a set of presuppositions is to examine the reasonableness of the conclusions that they entail. In any logically valid argument, the conclusion follows from the premises. One must then either accept the conclusion or reject the premises. To make a rational choice, one must ask: what is more plausible, that the premises are true or that the conclusion is false?

Often, of course, our comparison of plausibility is itself rather subjective, colored by our worldview. Sometimes, however, the conclusions are so strongly contrary to common sense that the choice should be clear. In that case, we have a reductio ad absurdum of the premises.

Consider, for example, George E. Moore’s refutation of Hume’s skepticism:

It seems to me that, in fact, there really is no stronger and better argument than the following. I do know that this pencil exists; but I could not know this, if Hume’s principles were true; therefore, Hume’s principles, one or both of them, are false. I think this argument really is as strong and good a one as any that could be used: and I think it really is conclusive. In other words, I think that the fact that, if Hume’s principles were true, I could not know of the existence of this pencil, is a reductio ad absurdum of those principles. (2)

Moore argues that, since it is more certain that his pencil exists than that Hume’s premises are true, Hume’s set of premises must therefore be rejected as false.

Moore’s argument is like that of Aristotle, in Physica, who met the skepticism of his day with the reply:

That nature exists it would be absurd to try to prove, for it is obvious that there are many things of this kind and to prove what is obvious by what is not is the mark of a man who is unable to distinguish what is self-evident from what is not. (3)

In brief, if the falsity of the conclusion is more plausible than the truthfulness of the premises, then it is rational to reject the premises. This is particularly the case if the conclusions deny that which is directly evident to our senses. After all, worldviews are supposed to explain our observations. If any theoretical explanation is at odds with our personal experiences, then it is clearly the explanation, rather than our experience, that will have to be revised. The advantage of this method of refutation is that one need not pinpoint exactly where the initial error occurred.

3. Impossible to live out

Hume’s skepticism fails also the test of livability. Consider, for example, Hume’s own writings on skepticism. Surely Hume, by writing and publishing arguments for skepticism, expected others to read and comprehend them. This, in turn, assumes the existence of an external world consisting of at least paper with symbols on it, as well as other minds to whom the symbols on the paper are directed. It assumes further that, in reading Hume’s book, the senses of other people will reliably transmit to the mind what is written down. Hence Hume’s written defense of skepticism is self-refuting. Hume’s book itself refutes the theory of mind it contains.

Indeed, Hume confessed his own inability to consistently maintain his skepticism:

The great subverter of Pyrrhonism or the excessive principles of skepticism is action, and employment, and the occupations of the common life. These principles may flourish and triumph in the schools; where it is, indeed, difficult if not impossible to refute them. But as soon as they leave the shade, and by the presence of the real objects, which actuate our passions and sentiments, are put in opposition to the more powerful principles of our nature, they vanish like smoke, and leave the most determined skeptic in the same condition as other mortals.…

Nature is always too strong for principle. And though a Pyrrhonian may throw himself or others into a momentary amazement and confusion by his profound reasonings; the first and most trivial event in life will put to flight all his doubts and scruples.… When he awakes from his dream, he will be the first to join in the laugh against himself, and to confess that all his objections are mere amusement…(4)

Hume’s failure to integrate skepticism into his daily life is itself the practical refutation of skepticism. Deeds, not words, are the most telling indicator of a philosopher’s deepest convictions.

Hume conceded that “custom…is the great guide of human life.”(5) Only Hume’s habits of mind enabled him to accept such things as, for example, the principle of causality whereby he could successfully navigate life. However, he was unable to give these a rigorous philosophical grounding in terms of his empirical presuppositions. Hume’s skeptical worldview failed to adequately account for the reliability of such common-sense knowledge.

The dilemma of relativism is that it asserts a non-relative claim, which inevitably leads to its self-refutation. As Thomas Nagel notes:

The claim “everything is subjective” must be nonsense, for it would itself have to be either subjective or objective. But it cannot be objective, since in that case it would be false. And it cannot be subjective, because then it cannot rule out any objective claim, including the claim that it is objectively false. (6)

Similarly, the skeptical claim “there is no objective truth” is itself a truth claim, contradicting itself.

If relativists were consistent with their professed beliefs, then they would have to remain silent. Skepticism renders philosophical discourse null and void. Hume concluded his Enquiry Concerning Human Understanding with the following advice on how to choose books:

Does it contain any abstract reasoning concerning quantity and number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion. (7)

Unfortunately for Hume, this severe standard dooms his own works to ashes.

In sum, a worldview may be assessed directly, by examining the plausibility of its presuppositions, or indirectly, by considering the consequences of its set of presuppositions. It is irrational to accept a worldview whose consequences are less plausible than the denial of one or more of that worldview’s presuppositions.

Extreme forms of skepticism or relativism cannot be rationally defended. Any viable worldview must allow for (and justify), at least to some extent, objective logic and language, as well as other factors that are presumed in normal intellectual discourse. The relativist may claim that he is not concerned with rationality or consistency. He may prefer to live inconsistently rather than opt for another worldview. However, this amounts to giving up on explaining reality and resigning oneself to superficiality.


1) Aristotle. 1952. The Works of Aristotle Vol.I. [Great Books of the Western World Vol.8]. Robert M. Hutchins (ed.). Chicago, IL: Encyclopaedia Britannica, p. 362.
2) Moore, George E. 1953. Some Main Problems in Philosophy. New York: Collier, pp. 119-120.
3) Aristotle. 1952. The Works of Aristotle Vol.I. [Great Books of the Western World Vol.8]. Robert M. Hutchins (ed.). Chicago, IL: Encyclopaedia Britannica, p. 268.
4) Hume, David 1777. An Enquiry Concerning Human Understanding. La Salle: Open Court (1958 reprint), pp. 177-179.
5) Ibid., p. 47.
6) Nagel, Thomas. 1997. The Last Word. New York: Oxford University Press, p. 15.
7) Hume, op. cit., p. 184.

This is an excerpt from Dr. John Byl’s apologetic classic “The Divine Challenge: on Matter, Mind, Math & Meaning” which he’s just updated, and made freely available via his website It is reprinted here with the author’s permission.

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Free book: The Divine Challenge: on matter, mind, math & meaning

Christians believe the world, the universe, and everything came about by Supernatural means – our God created! Those that deny the supernatural say that the universe came about only by natural processes – mere physics and chemistry, over eons of time. Is this a debate to explain why there is something, rather than nothing? No, says John Byl, the real question is “Who will rule: God or Man?” And in the world’s attempts to usurp God, they’ve crafted many a worldview to try to explain things apart from Him. In his brilliant apologetic work The Divine Challenge, Dr. Byl shares the world’s best godless worldviews. He shows, often in the proponents’ own words, how their explanations are self-contradictory or simply fail to explain what they set out to explain. Naturalism says there is nothing outside of nature, and materialism that there is nothing outside matter, so how can either explain how matter came to be, or the non-material world of math and meaning? Byl also makes evident how very often these godless philosophers understand the emptiness of their best answers, and yet cling to them anyway because they hate the alternative: bowing their knee to God. This is a book that will stretch most readers, and in some parts (Chapter 14 was a doozy!) I only got the gist of it. But what an encouraging gist it was! While the 2004 paperback edition is still available, Dr. Byl has made his 2021 revision a free ebook you can download at his site here:

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