I read some people don't believe in truth but do believe there is always a chance that x. I have a question about such thought.

I recently heard an anecdote that says nobody can ever prove I ate yoghurt this morning, even when there are thousand pointers that hints to the facts I actually did ate it. For example,multiple people who were with me this morning could confirm it; but they could lie. You could see the pack and see there is yoghurt missing; but it never proves it was from me. There could be photos and videos seeing me eating the yoghurt; it could be photoshopped or material from yesterday. Even if they open my body and find yoghurt, the chances are never 100% it was me eating the yoghurt. Because there are always questions/reasons it didn't. It seems it can never be proved.

Does that mean we can never ever prove something is real, or really happened? And if that is true, can't we also never prove something isn't real?

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    close vote - primarily opinion based :-P May 12, 2015 at 13:05
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    Even if you are totally convinced that you did eat yoghurt this morning, perhaps you have just put your spoon down and can still taste the last mouthful, it is still possible that you are imagining it and in a few minutes you will wake up from this strange dream and find that actually you are eating something else. May 12, 2015 at 13:59
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    "Even if they open my body and find yoghurt, the chances are never 100% it was me eating the yoghurt." And quite more it is hard to proof it was this morning ;D
    – Zaibis
    May 12, 2015 at 14:32
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    I once had a dream that Aristotle explained his philosophy to me, and I refuted it. Then Plato did the same, and I refuted it. Then all the great western and eastern philosophers appeared, and I refuted all their philosophies. I woke up and wrote down the refutation, and went back to sleep. In the morning I found that I had written down OH YEAH? THAT'S JUST YOUR OPINION BUDDY. May 12, 2015 at 15:37
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    I like this question! Is it that the notion of proving something is born out of mathematics/logic, which is only a representation of our percieved reality ? That is, the concept of proving something doesn't have a place in the world before us ? In the 'real world' you can only observe effects and demonstrate repeately (scientific method). May 13, 2015 at 10:06

11 Answers 11


This is why people invented words like "probably": if a man habitually has yoghurt every morning then tomorrow morning I expect him to have yoghurt at breakfast though of course there is a small chance that he might not.

That small chance is where the attention of scepticism directs itself; scepticism by itself - pure sceptism otherwise known classically as Pyrrhonism - doesn't get you very far; as a tool it's useful, and sometimes pointless; one requires judgement - which Kant designates as the highest faculty of man as a rational being.

Doubt as a method possibly attracts more attention than it deserves probably because of how Descartes used it; and it appears to have been welded into mathematics and the sciences as an indispensable method; and so it is - but it should not at the expense of other methods such as reasoning by analogy.

Kierkegaard for instance was scornful of these disciples of Descartes whilst approving of Descartes himself - as his use of doubt was 'honest'; a means towards something; it was a positive project - an epistemology; he was a yes-sayer rather than a nay-sayer who use doubt as a child might use it - saying "no this can't be true" and "no, nor can that"; and "nothing can be true when everything can be true".

Pick up an apple; doesn't it feel real? Well then it is real; when philosophers talk about the reality of things, they often use the word "real" in a sense different to what we normally think it; a classical example is to interpret "real" as "that which is permanent and eternal"; the apple is not real in this sense - you might eat it; in this sense we have the Parmenidian One, atoms - ie quarks, or God.

  • Thank you for this answer. It helps me thinking that scepticism doesn't take me very far. Also I think it is wise to keep things in perspective, the apple example has good points.
    – Mark Knol
    May 15, 2015 at 21:05

One group of thinkers who thinks along those lines are Bayesians. For Bayesians, it's not so much that they think everything is an opinion, or that there is no truth, rather it's that their framework around learning the truth does not allow for certainty in the truth. There is a practical reason for this: every piece of data you receive should be able to change the likelihood of a statement.

Take for example your example statement:

I ate yogurt this morning

Given that you say you ate yogurt this morning, this statement becomes very likely. But how then do we process evidence that points to the contrary? What happens if someone says that you didn't eat yogurt this morning because you at it this afternoon?

Another aspect of the Bayesian approach, however, is that we in general are forced to make specific decisions about reality. So, for example, maybe we are forced to bet with someone else whether you ate yogurt this morning: as a practical matter, this uncertainty often collapses to needing to make a particular decision.

  • 1
    "... their framework around learning the truth does not allow for certainty in the truth." It does - in fact it must in any well-defined probability problem. The probabilities of all the possible mutually exclusive outcomes have to add up to 1, so the probability that any one of them happens (which is a certainty) must be 1. May 13, 2015 at 14:52

It depends on your definition of proof.

Proof in everyday usage is just some sufficiently convincing evidence, and what is sufficient depends on the person who wants proof of something. For most people there are many things that can be proven beyond reasonable doubt. For example, the earth is not flat and the planets in our solar system orbit the sun and not the earth. For another example, you were not constructed just one millisecond before the present moment and implanted with memories that fool you into thinking that you have been alive for a long time. (Wait a second and consider this possibility again! Maybe just before now you were constructed and implanted with the memory that you were reading about this...)

However, if you take the most stringent possible definition of proof, an argument that can under no circumstance be incorrect, then there are not many things that can be proven. One example is the fact that something exists. No matter what, this present fact cannot be denied, even if we cannot absolutely prove much about what kind of thing exists.

Even mathematical proof is not absolute, but is just a sequence of logical deductions, each one based on axioms or prior deductions and derived by some inference rule. A mathematically proven statement would be absolutely correct if all the axioms and inference rules used in the proof are first accepted as absolutely correct. That is the whole purpose of creating formal systems, so that anyone who accepts all the axioms and inference rules will have no choice but to accept all the statements proven within the formal system. The fact is that without any inference rule, there can be no formal proof at all. And the less axioms are accepted, the less can be proven. One must start with at least one initial assumption otherwise one gets nothing. Incidentally, essentially all formal systems include the assumption that something exists in the universe of discourse, because otherwise there is nothing to talk about and no reason to talk at all!

That said, there is an underlying explanation as to why some people as you describe do not believe in truth and yet believe that there is always a chance for anything to happen. First one must make a distinction between people who believe that there is an absolute truth that is inaccessible and people who believe there is not even absolute truth. The former is reasonable, but the latter is not, because it is inconsistent. The very concept that there is no absolute truth is itself an absolute concept, and so if it were true then by itself it cannot be absolutely true, which is self-contradictory.

Note that one must also avoid the fallacy that anything that is possible must happen, since it is equally self-contradictory. Specifically, it is possible that not everything possible does happen, which would contradict that fallacy if it were true. Therefore it cannot be true.

Therefore it does not make sense for people to claim that there is a chance for everything, because given any statement that is precise and well-defined in its context, either it is true or it is false. The fact that we are normally rather imprecise, due partly to our use of natural language, does not mean that one is justified to disregard everything that anyone else says. Rather, one ought to make a reasonable attempt to figure out the underlying precise statement before attempting to judge whether it is true or false.

Such claims of the complete subjectivity of truth are often because they either do not want to care about the truth or falsity of the statement under consideration, since it takes a lot of time and effort to investigate truth, or they have ulterior motives in affirming certain so-called possibilities.

The clearest examples of instances of people evading the truth are precisely the ones concerning important truths, such as moral atrocities. Usually, the perpetrators and others who have vested interests in covering the truth up will continually and vehemently deny, and sadly in some cases the truth is gradually lost over time.


Does that mean we can never ever prove something is real, or really happened?

You can prove the existence and reality of thought.


I think you can get most "people that don't believe in truth" to accept that thought exists.

And if that is true, can't we also never prove something isn't real?

It is left an as an exercise to the reader to envision something that contradicts the possibility of thought, and conclude that it isn't real because thought is real.


Your question presupposes that proving ideas true or probably true (justification) is the standard of rationality. That assumption is false.

As Popper pointed out in Chapter I of "Realism and the Aim of Science" justification is impossible, unnecessary and undesirable. If you assess ideas using argument then the arguments have premises and rules of inference and the result of the argument may not be true (or probably true) if the premises and rules of inference are false. You might try to solve this by coming up with a new argument that proves the premises and rules of inference but then you have the same problem with those premises and rules of inference. You might say that some stuff is indubitably true (or probably true), and you can use that as a foundation. But that just means you have cut off a possible avenue of intellectual progress since the foundation can't be explained in terms of anything deeper. And in any case there is nothing that can fill that role. Sense experience won't work since you can misinterpret information from your sense organs, e.g. - optical illusions. Sense organs also fail to record lots of stuff that does exist, e.g. - neutrinos. Scientific instruments aren't infallible either since you can make mistakes in setting them up, in interpreting information from them and so on.

We don't create knowledge (useful or explanatory information) by showing stuff is true or probably true for reasons so how do we create knowledge? We can only create knowledge by finding mistakes in our current ideas and correcting them piecemeal. You notice a problem with your current ideas, propose solutions, criticise the solutions until only one is left and then find a new problem. We shouldn't say that a theory is false because it hasn't been proven because this applies to all theories. Rather, we should look at what problems it aims to solve and ask whether it solves them. We should look at whether it is compatible with other current knowledge and if not try to figure out the best solution. Should the new idea be discarded or the old idea or can some variant of both solve the problem?

When should you say something is real, or that an event happened? When the only existing explanation that has survived criticism is that the thing in question is real or the event happened.


Such questions are dealt in the branch of philosophy known as Epitemology

Bertrand Russell, the famous mathematician and philosopher, did some good work in this branch. His book "Problems of Philosophy" is primarily targeted at uncovering the nature of "truth".

He starts off with this question :

Is there any knowledge in the world which is so certain that no reasonable man could doubt it?

In his book, he discusses the method of Descartes of "systematic doubt". He discusses how Descartes reached to the conclusion that the only truth that he could be certain of was of his own existence. This thought of Descartes is summarized as:

I think, therefore I am

You could download the book freely (and legally) from here:



I don't think everything is necessarily opinion. If two people have a close enough understanding of the premises of an argument/question, there definitely can be definitively right and wrong answers. That being said, one could argue that the spectrum conceptual synonymy is infinite.


nobody can ever prove I ate yoghurt this morning

Do you mean "prove to yourself" or "prove to others"?

The question arises e.g. with the Theory of Evolution: "If the earth is really only 6000 years old, then when were the dinosaur fossils created?" etc.

Some of the "laws" are better-proven than others. The law of gravity, for example: if I drop a hammer on my foot, I can entertain the thought that perhaps it will float like a feather in the air instead of dropping, BUT I am what I call "virtually certain" that it would drop and hurt and therefore I won't try it.

I suppose I'm used to the notion that I might be wrong. I like to think that I'm "biased" but not "prejudiced" i.e. that if NASA would demonstrate an anti-gravity device then my bias would say "that's highly unlikely to be true" but I wouldn't have prejudice saying "that's impossible".

So maybe I use fuzzy instead of boolean logic: the probability of the hammer hurting my foot if I drop it is ninety nine point nines percent, not a hundred. Still that's close enough to a hundred that I won't make the experiment.

Note that criminal law has to cope with this kind of problem too, so apparently it uses notions like "evidence" and "beyond reasonable doubt".

  • The proper use of science is to make predictions about observable future phenomena. A proper scientific statement by a geologist shouldn't really be "A gold-bearing river flowed here", but rather "If you dig here, you'll likely find gold deposits similar to what a gold-bearing river would have produced." To be sure, the most logical explanation for why one would find such deposits would be that a gold-bearing river had flowed in the area, but one can't prove that in the same way as one can prove one's ability to predict where diggers will find gold.
    – supercat
    May 12, 2015 at 14:57
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    @supercat - There is nothing about the logical structure of knowledge gained from science that prevents you from reliably assigning historical causes. Some history (e.g. an ocean liner sinking to the sea floor 15 seconds ago) just leaves more reliable evidence than others (e.g. a jellyfish on the sea floor from 600 million years ago).
    – Rex Kerr
    May 13, 2015 at 9:00
  • For example, pathology: "In his roles as a pathology instructor and as medical examiner for Shelby County and the State of Tennessee, Francisco estimates he has seen 30,000 to 40,000 dead people in his life. Elvis, he says, fit the profile."
    – ChrisW
    May 13, 2015 at 9:07
  • @RexKerr: If a wrecked ship is found on the ocean floor bearing the name "RMS Acme", that would suggest that the RMS Acme sunk there. It would not, however, rule out the possibility that some person or entity decided to plant fake evidence of the RMS Acme having sunk there. Returning to the gold mining example, it would be possible that some aliens with a gold transporter ray planted gold deposits in ways they thought were aesthetically pleasing. Even if that were so, however, it would not imply that mining practices should change, since what was thought to be evidence...
    – supercat
    May 13, 2015 at 15:28
  • ...of gold-bearing rivers would instead be evidence of places that the aliens would consider aesthetically suitable for planting gold deposits, and in either case the proper action would be "dig here". Unless or until a means can be formulated to distinguish the action of aliens from that of an ancient river, the "aliens" theory would be non-falsifiable and thus non-scientific, but that wouldn't mean the scientific "ancient rivers" theory was correct and the aliens theory was wrong; merely that the "ancient rivers" theory could be more readily used to make good predictions of where to dig.
    – supercat
    May 13, 2015 at 15:37

You guys upvoters on this question ( I did not ) in my personal opinion owe some moral responsibility, I think. Personally, I am taking this one of kind of an insult on all the answerers.

I would like to quote 19th century materialist Joseph Dietzgen

From his The Nature of Human Brain Work

In its universal search from the attribute to the substance, from the relative to the absolute, from the appearance of things to the true things, the mind finally arrives at the understanding that the substance is nothing but a sum of attributes collected by brain activity, and that the mind itself, or reason, is a substantial being which creates abstract mental units out of a multitude of sense perceptions and conceives of the universe as an absolute whole, as an independent “thing itself,” by adding all its transient manifestations. In turning away full of dissatisfaction from attributes, searching restlessly after the substance, throwing aside phenomena, and forever groping for truth, for the nature of things, for the “thing itself,” and in finally realizing that this substantial truth is merely the sum of all socalled untruths, the totality of all phenomena, the mind proves itself to be the creator of the abstract concept of substance. But it did not create this concept out of nothing. On the contrary, it generated the concept of a world substance out of attributes, it derived truth out of manifestations of things.

The idealist conception that there is an abstract nature behind phenomena which materialises itself in them, is refuted by the understanding that this hidden nature does not dwell in the world outside of the human mind, but in the brain of man. But since the brain differentiates between phenomena and their nature, between the concrete and the general, only by means of sense perception, it cannot be denied that the distinction between phenomena and their nature is well founded; only the essential nature of things is not found back of phenomena, but by means of phenomena. This nature is materially existent and our faculty of thought is a real and natural one.

And you question,

Does that mean we can never ever prove something is real, or really happened? And if that is true, can't we also never prove something isn't real?

Now, if you read the bolded parts of the sentence, according to Dietzgen, ( he is reffering to Kant, actually ), one does not always need to "search for thing-itself". But rather, if one wishes to feel or sense the objects outside him or her, only what he or she simply needs to do feel or sense the sub-categorized "phenomena, or the properties of thing-itself, since after all, we are not able to reach the thing-itself. ( But be reminded Dietzgen limits such activities should be only applied to sensing or feeling phenomena, putting aside thing-itself. )

So according to Dietgen, only what we, human being need to know, or sense something, while we are living, is just to sense or feel the phenomena or properties of the thing-itself, and he says that is enough for human beings, since after all, what can we gain by "searching for thing-itself"??

So I am sorry to use this word, but have to resort to, proving if it is real or not is just, unnecessary for human beings.


In the 'real world' you can only observe effects and demonstrate repeately (=scientific method). Therefore, nothing in the real world can be proven.

Proof is a mathematical/logical concept - as maths and logic describe a model of the world, proof really only demonstrates that that model is correct, not the real world.


I think "always a chance that not X" means that X is not apodictic.

apodictic ˌapəˈdɪktɪk adjective formal clearly established or beyond dispute.

It is a term that I only ever read encountered in Husserl, and therein I think he means what we establish which we will never have to go back to and double check our reasoning. Whether anything has this quality is IMHO moot - possible the cogito [I think therefore I am] at least on the assumption we can make sense of the argument. Naturally, Husserl thought there was a lot of apodictic knowledge, including IIRC the need for his own phenomenology, and so forth.

Of course there are weaker forms of knowledge, and I would assume that a lot of mathematical proofs are necessarily true but we (certainly I anyway) couldn't claim to have settled their factual correctness beyond dispute.

And then of course there is justified belief - when something seems so likely that rejecting it is almost absurd. An example that springs to my mind is that there are no miracles, though this is a source of disagreement for some, so could legitimately be called an "opinion" - if that is taken to mean contested rather than unjustified.

In conclusion, it depends on what you mean by "opinion" and if you mean that nothing can be justified then you are incorrect, whether or not I now justify that!!

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