Would it be sensible to say "I know Santa does not exist", and more generaly, what do we really say when we say "I know that [some fact]" ?

It is a well known principle that "absence of evidence is not evidence of absence". As such, we have no evidence Santa does exist, but also no evidence he does not.

Yet, I feel comfortable saying I know that Santa does not exist, below are my reasons and I would like to know if the reasoning is sound, and if possible references of authors who have written on the topic.

To be specific, let's consider we speak about the classic Santa, who has a base at the north pole, knows who have been naughty, receives letters and deliver presents to all the kids, during the night from 24th December to 25th, directly in their home by the way of a flying sled.

This Santa surely breaks all the laws of physics, and the probability that he can fly a sled at mach 30 at low altitude without notice is incredibly low. Nothing of the sort has ever been witnessed as far as we know. If we take as a definition of "I know X"="I hold X to be true and I have good reasons for it", then I surely hold the inexistence of Santa to be true, and i have as good reasons as can be for it.

I heard the argument that these are good reason to not believe Santa exists, but you can't say you know. However improbable, it's impossible to totally rule out the possibility that he has a crazy secret technological or magic trick that lets him deliver the presents every Christmas. There is still a probability that I am wrong, still a possibility that some day someone produces evidence for Santa and I will have to change my position. Therefore "not believe" is said to be the correct phrasing.

Yet, if i compare with other facts I know, and nobody would ever contradict me if I say I know them, I can't see the difference.

For example if I say "I know I was born the 12th of March", nobody would ever dare to say "oh no, you believe you are born the 12th, but there is still a chance you might be wrong". Yet, if we are to be rigorous about it, it is still possible, albeit improbable, that someone someday brings official papers, the testimony of the midwife, the maternity archives demonstrating that I was in fact born the 15th, and I was wrong this whole time. Administrations make mistakes, so there is a possibility that I will someday have to change my position about this fact I know.

To be honest, I would be less surprised to learn that I was mistaken about my birthday, than I would be surprised to meet Santa. As in orders of magnitude less surprised. So if I can say "I know i was born the 12th of march", why can't I say "I know Santa does not exist" ?

Edit: This question is not so much about "absence of evidence is not evidence of absence", but the value of the expression "I know that...". Why is it trivially accepted for some facts (birthday), and usually rejected for others (the existence of Santa) ? Is there some kind of epistemological difference between the two facts, that justify this, or are people just shying away from what they perceive as too bold a statement ? And if the mere criterion that I think I have good reasons is enough to justify me saying "I know Santa does not exist", how is it different from a madman who thinks he has good reasons to believe there is a pink dragon in his garage ?

  • It is absolutely correct to say "I know Santa does not exist", if you know - as it seems - that "Santa does not exist". And "Santa does not exist" is true simply because Santa does not exist. Apr 13, 2019 at 9:28
  • "It's impossible to totally rule out the possibility" is certainly not how the word "know" is normally used, as well as a wrong standard for knowledge philosophically, see Reliabilist Epistemology. The "absence of evidence is not evidence of absence", taken naively, is also false, and its refinements do not apply in the case of Santa and the like, see Absence of evidence is not evidence of absence.
    – Conifold
    Apr 13, 2019 at 11:31
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    Possible duplicate of Absence of evidence is not evidence of absence
    – Conifold
    Apr 13, 2019 at 11:31
  • You may be talking about the difference between relative and absolute knowledge. We tend to sloppily elide the two in ordinary conversation and use 'know' to describe what is actually just our best theory. I feel that despite Descartes many philosophers tend to forget to make this distinction and think they know more than they do, and among Joe Public it's an epidemic. . . ,.
    – user20253
    Apr 13, 2019 at 14:06
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    @user4894 I always told my 8 years old that Santa was myth, he never believed in him and is happy with his presents nonetheless. The probleme is not the reveal, it's the intoxication ^^
    – armand
    Apr 14, 2019 at 11:54

6 Answers 6


This is a question of the foundation of any knowledge. How do we know anything? Because it could always be the case that we are dreaming, mistaken, a brain in a vat, Truman Show scenario, the world is not as it seems at all, etc.

What I prefer to do is to think of the very "know" with two basic levels:

  1. Know in an everyday level. In this level, I know Santa Claus doesn't exist, for all the obvious reasons you cited in your question and many others. Note: knowing something at this level shouldn't always be so trivially easy as with the Santa Claus case; a careful thinker should be reticent to state he or she knows something about the world in many cases. I prefer to say, "To the best of my knowledge" for many subjects.
  2. Know in a philosophically strict level. In this level, I don't know much at all--perhaps nothing. Certainly not that Santa Claus doesn't exist.

Bertrand Russell makes this point about philosophical strictness, in this case in reference to the existence not of Santa Claus, but gods:

“I think that in philosophical strictness at the level where one doubts the existence of material objects and holds that the world may have existed for only five minutes, I ought to call myself an agnostic; but, for all practical purposes, I am an atheist. I do not think the existence of the Christian God any more probable than the existence of the Gods of Olympus or Valhalla. To take another illustration: nobody can prove that there is not between Earth and Mars a china teapot revolving in an elliptic orbit, but nobody thinks this sufficiently likely to be taken into account in practice. I think the Christian God just as unlikely."

  • Descartes tried to identify what we can know in the philosophical level, and did not find much. We know that we are, period. That raises the question of how much value we can give to a concept of knowledge so strict we can know only one fact.
    – armand
    Apr 15, 2019 at 0:39

You do not know that Santa does not exist. Bornat indicates the central reason:

But how could I disprove the existence of somebody, like Santa Claus, who nobody has ever seen and who most of us believe doesn't exist? With great difficulty: I would have to look everywhere and fail to find him anywhere. I would have to look everywhere all at once, because he might flit from place to place, evading my search. But even if I discount flitting — after all, he is supposed to sleep most of the year — we haven't yet looked everywhere [...], and in practice we never could. So we can't in practice disprove the existence of Santa Claus (Bornat 2005, p. 103).

On this basis, you cannot know on empirical grounds that Santa does not exist. You appeal to the laws of physics in respect of one alleged attribute of Santa but these laws are not known to be true. They are at best universal, falsifiable empirical generalisations (or propositions) which it is currently rational to believe or provisionally to accept hypothetically.

Only if the specification of Santa's essential nature or defining attributes involved a contradiction could you know that Santa does not, because logically could not, exist. But you offer no such specification.


Bornat, R. (2005). Proof and disproof in formal logic. Oxford: Oxford University Press.

Mion, G. 'God, ignorance and existence', International Journal for Philosophy of Religion, Vol. 72, No. 2, Logic (October 2012), pp. 85-88: 86.

Objection 1

Well, I feel like I can respectully disagree with Bornat. I don't need to search the whole universe before ruling out the existence of Santa: for him to exist as I defined him in the question, that would require hypersonic stealth flying deers that conflict with a very well established and thoroughly tested corpus of physics knowledge. This is why I would be more surprised to find him than to learn I was mistaken about my birthday. Yet nobody would argue that I don't know my birthday. – armand

Reply 1

You are assuming that you know the truth of the relevant laws of physics. How could you possibly know this, however reasonable it may be to assume those laws as hypotheses in the present condition of science ? Also, I'd add that if you know that Santa does not exist, on the basis of scientific knowledge, what is the point of asking the question on a philosophy site ?

Objection 2

This is a question about epistemology, which is a branch of philosophy. I don't quite understand the dichotomy you are making between science and phylosophy, as the two discipline work together. Of course, I can't possibly know the real laws of physics, but the few that i know has been thoroughly tested across human history and is highly reliable. And it tells me that Santa can't fly a wooden sled with deers accross the world in one night, the same way i know Hussein Bolt can't jump to the moon (or would die in the process). – armand

Reply 2

Epistemology is indeed a part of philosophy and I do not dichotomise philosophy and science in any way that creates a rupture between them. Point is, you are not asking the question philosophically but scientifically. You raise a question and give a purely scientific answer. An epistemological answer would not appeal, as yours does, to what we know on the basis of science, but to the logical status of scientific laws, to the probative grounds (inductive or stronger or other) on which such laws are 'highly reliable', to the model of induction you are using if you choose inductive grounds, to the impossibility (Bornat's point) of confirming any such universal existential generalization as a scientific law and so on and on. Philosophy may as Quine held be continuous with science but its continuity consists in its raising extra issues such as these, which make no appearance in your answer.

I am enjoying the argument but can't, I'm afraid, see any reason to retract my answer.

  • That raises the question to know if formal logic is a proper tool to know reality, which I didn't think about at first.
    – armand
    Apr 14, 2019 at 11:58
  • Now, it COULD be possible that Santa has some kind of technology I don't know allowing him to fly his sled. Yet this is astonishingly improbable. Much more improbable than my being wrong about my age or even the color of my eyes, facts in regard to whuch nobody would contradict me for saying that I know them. Hence my being puzzled.
    – armand
    Apr 14, 2019 at 14:54
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    @armand. I have included your objections and given my replies in the revised text above. We are engaged in a civilised exchange of views, and I appreciate the time you have given to my answer. Best - Geoffrey
    – Geoffrey Thomas
    Apr 14, 2019 at 15:37

The appropriateness of using the locution "I know that Santa does not exist" depends, I think, on the context. In some situations, more appropriate. In some situations, less so.

The OP asserts with good reasons, that the proposition that Santa does not exist is highly probable [1]. Even, very highly probable. The OP also demonstrates that the proposition that Santa does not exist is not certain. Not as certain, anyway, as the proposition "2+5=7".

The term "knowledge" often indicates assurance. Sometimes, mere subjective assurance ("I just know that she did this!"). An objectively provable high probability is a better ground for assurance. But even this is not always enough. Philosophical discussions are, at least sometimes, more demanding ("Do we really know that Santa doesn't exist?"). Debates on sensitive issue, such as religious and ideological views, also can be demanding in such a way. When we debate against stubborn opposition or suspicion, even the slightest careless inaccuracy can undermine any chance of agreement.

'Knowledge' is, I think, a blunt and imprecise word, because it's binary. We either know, or don't know. There is nothing in the middle. We don't assign degrees to strength of knowledge. But we do assign degrees to strength of assurance, to strength of belief, to strength of justification. Therefore these latter terms are often better choices, if we care to exercise more precision.

[1] Which also touches on the question, what does "probable" mean here?

  • it could be argued that 2+5=7 is just a derivation of the definitions of two, five and seven, and we are 100% certain of it only because we defined it to be so in the first place. I don't think it is equivalent to actual facts of the world like "I was born 12th of june" or "there is a Santa", for which practical knowledge seems to be the best we can hope for.
    – armand
    Apr 16, 2019 at 0:41
  • @armand I didn't write that 2+5=7 is equivalent, but that it is more certain, than p = "Santa does not exist". If 2+5=7 is a consequence of definitions, it is still more certain than p. Therefore, what I wrote stands, either way.. Apr 16, 2019 at 4:41
  • @armand It just serves to show that there are different degrees of certainty. Apr 16, 2019 at 6:03

You can say "Santa does not exist in such-and-such place" because you have verified the place where Santa was not found. The number of places, at certain times, can grow, but it can never be topped out. But you can't validly say that "Santa does not exist" period, since you'd need to check all existent places and all existent times.

Now there are semantic arguments (vacuous validity) you can cite. If I say, "my apple exists" I don't need to make it exist at all places and all times, it just needs to exist in one place, at the current time. I don't need to say "my apple exists now at such-and-such place", "my apples exists" is enough to say and is valid even without presenting the specific information. Even though this is precisely the logic that is used in the first paragraph (Santa can exist in a singular place so you can't say "Santa existing is invalid" without checked all places), this leads to a funny conclusion: you can say "Santa doesn't exist" and still be valid since you don't need to provide the specific information about where Santa doesn't exist. But that's kind of meaningless to say since then every thing that does not exist in all places can be validly said to not exist. It's what we call vacuity.

  • you can't validly say that "Santa does not exist" Why ??? Santa does not exist; thus, we have to say that he does not exist. Apr 13, 2019 at 15:21
  • "every thing that does not exist in all places can be validly said to not exist. It's what we call vacuity." What does it mean ? Apr 13, 2019 at 15:22
  • @MauroALLEGRANZA, there must be some confusion here. "Santa does not exist in the place you are checking" is valid. "Santa does not exist" is only vacuously true just like "My apple exists" is. "My apple exists in my bag" is valid. "My apple does not exist" is a vacuously true statement derived from "my apple does not exist in my pocket." You can't say "Santa does not exist in any place" since that would invoke induction. Since my apple exists in only one place, I can say "my apple does not exist" by implicitly pointing to one such place where my apple does not exist. It's vacuous. Apr 13, 2019 at 17:20

If Santa is by definition considered a fictional character, as we know from historical evidence like these 19th century poems, then we can say that we know he does not exist. But this is not the same as saying we know there are no Santa-like entities in the real world.


Yes, questioner, there is a Santa Claus. According to David Lewis ("On the Plurality of Worlds") Santa does exist in some possible world and all possible worlds are "real"....

  • In that case is it possible there is a world where my mother in law does not bicker about everyone and his cousin? Because that sure does not feel real.
    – armand
    Apr 19, 2019 at 6:43
  • You may have just conclusively refuted Lewis.... Apr 20, 2019 at 0:48

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