It seems to me that this avoids the self contradictory "everything is uncertain, even uncertainty" while allowing agnostic positions, by allowing only uncertainty as the only thing certain, sort of the base case for everything.

Edit: Based on the first answer, the way I would formalize is: "Certain(x)" and "x = !Certain(y)" where "y = !x"

  • 4
    "Everything is uncertain except for this one claim" avoids the incoherence, but it is what is called special pleading, an unmotivated exception. One can make all sorts of self-consistent claims, e.g. "everything I say is true", the trick is to make them plausible. How one would do that when everything else is uncertain is very obscure. Skeptics typically avoid the incoherence by avoiding any claims, they express doubts about all of them, but claim nothing.
    – Conifold
    Commented Aug 26, 2019 at 4:25
  • 1
    If you admit ideal contents, you lose to analytic tautologies. That you cannot choose an element of an empty set remains certain. If you are talking about physics, you have a category problem, certainty or uncertainty is part of our thoughts about physical facts, and not part of the physical world, so the principle of uncertainty does not apply to it to begin with. Instead of a correction, this makes for a statement that is to some degree meaningless.
    – user9166
    Commented Aug 26, 2019 at 6:27
  • @Conifold, I believe that as well. But I see the statement more of as an axiom, since there is no guarantee that what we think of as logical and physical laws actually hold in all possible worlds across time, even though we strongly believe in them. I feel comfort that if doesn't contradict itself while expressing that notion.
    – csp2018
    Commented Aug 26, 2019 at 10:49
  • Logical laws govern only our language, not the world. But if you allow altering them, why care about contradictions? The law of non-contradiction need not be certain either. And calling a sentence "certain" makes it no more certain than writing "yellow" on a page makes it yellow. So why say it at all, let alone draw comfort from it?
    – Conifold
    Commented Aug 26, 2019 at 23:10
  • 1
    To doubt everything, or, to believe everything, are two equally convenient solutions; both dispense with the necessity of reflection. Instead of a summary condemnation we should examine with the utmost care the role of hypothesis; we shall then recognize not only that it is necessary, but that in most cases is legitimate.” • Henri Poincaré: Science and Hypothesis, 1905
    – user47436
    Commented Oct 19, 2020 at 7:14

2 Answers 2


Actually it may not be a contradiction:

  1. We are only certain of progressive change. This change manifests itself as the progression of one self evident truth to another: A -> B -> C...

  2. This progressive change observes a linear continuum, as one self evident truth progresses to another.

  3. This linear continuum, as progressive axioms, is constant in both an abstract sense and empirical time (ie one particle moving from one position to another always has a straight line between points even if the pattern is zig zagging.).

  4. This linear continuum observes form and function as the same thing. So while we may have variously changing self evident truths, these truths exist recursively under a single platonic form.

  5. Each change effectively is composed on infinite immeasurable changes (ie zeno paradox or a line composed of infinite lines) this necessitating infinite change as indefinite change or "no change.

  6. Change is that the observation of multiple parts. For example one picture inverting to another picture observes static pictures but the perceived movement only occurs because of the multitude of pictures. Change is thus grounded in the inversion of one phenomenon into many. One picture into another, the position of one particle into another position, one emotion into another emotion, etc.

  7. Change and no change, using a line as an example, is assumed through form alone. It is the dualism between one and many forms that allows change and no change to be observed. However this dualism is synthesized under the "form" itself as a "boundary of movement".

  8. This can be observed through the platonic forms as consisting of many forms or the process of actualization, in aristotelian thought, as matter existing through form where potentiality (ie mass) exists through form as movement.

I hope this makes sense, I may have to clarify some points.

  • Richard Feynman said that all scientific knowledge is uncertain and uncertainty is a very important part of it. He goes on to say that if we are free of doubt and ignorance, we will not get any new ideas and make no progress.ajnr.org/content/31/10/1767
    – user47436
    Commented Oct 19, 2020 at 7:54

Everything is uncertain, including uncertainty, for the simple reason that your brain is just a machine, and machines can fail for a variety of reasons. If you're willing to accept that something as simple as 2+2=4 is slightly uncertain (and you should be) then you should be willing to accept that the reason 2+2=4 is uncertain is also uncertain. Consider that "the reason 2+2=4 is uncertain" is significantly more complex reasoning than "2+2=4" itself, and more complex means more error-prone.

Anyway, why is everything uncertain? Because your brain is a machine, and machines are fallible. Let's start by looking at how silicon computers are fallible. Silicon computers are much more reliable at accurate math calculation than your brain is, and yet you cannot fully trust the result of a mathematical calculation done on a computer.

  • There can be software bugs causing inaccurate calculations. The types of bugs are too numerous to list, but can include failure to bounds check, failure to initialize, floating point overflows, rounding errors, prematurely freed memory, and on and on and on.
  • Someone could have hacked your system without you knowing, and maliciously altered your program to give you the wrong calculation result.
  • There can be hardware bugs causing mathematical failures, such as https://en.wikipedia.org/wiki/Pentium_FDIV_bug or others we may not know about.
  • Even if there are no hardware design bugs, there is always a chance of manufacturing defects, e.g. a stray bit of dust on the lens when engraving the wafer. The manufacturer tests for such defects but no testing process can give a 100% guarantee.
  • Cosmic rays or other radiation could have altered the functioning of the chip at a critical time
  • You may have undetected age-related failure in your computer's memory or hard disk
  • It's extremely unlikely, to the point that it's probably never happened in the history of computing, but there's still a nonzero probability that quantum tunneling of the electrons on your chip could alter the result of a calculation.

So those are some examples of how a machine can fail at any calculation. Your own brain is a machine too, and a much less precisely designed one than a computer. Your brain makes mistakes at a much greater rate than a computer.

  • Everyone is familiar with making arithmetic and logic mistakes on academic tests. Even when someone fully understands a subject, they still make mistakes due to inattention or dyslexia/dyscalculia. And people are not fully aware of when they are inattentive; that's another mistake we make.
  • Neurons operate probabilistically; action potential produces a chance of firing, not a certainty. This means that the result of any calculation done by neurons is at least partially random, and could randomly give some very incorrect result.
  • Cosmic rays have a chance to affect neurons just as they can affect computer chips
  • Neurons die, and sometimes are born. What if that happens in the middle of the calculation you're performing?
  • Artificial neural networks are trained in a process of trial-and-error, and the training may give good results but it does not result in a network with guaranteed perfect performance on a problem. If your brain's neurons are anything like that, they also do not have any guaranteed perfect performance.

Of course, if your brain's operation is fallible, then any calculation or reasoning you do mentally, no matter how simple, might in fact be an error, as it is the result of your brain's operation. You have no way of verifying or checking this reasoning except by ultimately relying on your brain, so any verifying/checking process is also fallible. Perhaps you can get very close to certainty, but it is irrational to suppose you ever have perfect certainty.

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