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How do I know if a piece of infromation is a fact or an opinion?

I read that facts can be proven while opinions can't, but for example if I say: "It is hot!":

It can be proven whether I'm really hot or I'm lying by observing sweat. Then all opinions can be proven; So, there are no opinions.

I also read that facts are absolutely accepted while opinions are relatively accepted, but for example if I say "Earth is an irregularly shaped ellipsoid.":

Some people will accept this, while some will reject it and accept that earth is flat. Then all facts will not be absloutely accepted; So, there are no facts.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Philip Klöcking
    Jul 25 at 17:01
  • Is fact vs opinion perhaps more like factual vs argumentative? Or positive vs normative? law.stackexchange.com/questions/1375/… then the scientist may make an objective claim...soooo a fact is not necessarily a 'true fact' ? idk i figured fact is actually an objective claim while an opinion is an actually a subjective claim...in your case re the life existed i think it's more of a guess or hypothesis or conjecture than an 'opinion' ? idk
    – BCLC
    Jul 25 at 21:24
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    Unfortunately, the "hot or not" question has a third option that can cause the observation to be incorrect, that the person isn't sweating because they are dehydrated. So, the person can be hot and not sweating. And the idea that some people refuse to accept facts (and refuse to learn enough to accept facts) doesn't prove there are no facts, just that some people aren't reasonable. Jul 26 at 16:46

13 Answers 13

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Few philosophers seem to have bothered with this particular distinction (as opposed to many lawyers). As a philosophical question it's confounded by several problems: fact vs. statement of fact, fact-value distinction, objective/subjective reality etc.

According to (American philosopher) John Corvino, one way to at least be less confused is to see the distinction as:

  • A statement of fact is one that has objective content and is well-supported by the available evidence.

  • A statement of opinion is one whose content is either subjective or else not well supported by the available evidence.

You still have to decide on those sub-criteria, which is not necessarily an easy task, depending on your philosophical standpoint on the sub-problems. (Well, he does assume a subjective/objective distinction is possible, just like most lawyers do).

But don't go to a court with this def. Because if you state a wrong fact about someone (meaning judged to be intended as statement of fact, but not a fact, i.e. false by the court), you're definitely much more likely to be liable for defamation than if you state a subjective opinion (in the court's view). In other words, the lumping of the two or-ed categories in the last bin (by Corvino) may be dangerous to your legal outcomes. But the lumping is reasonable for everyday use of the retort "it's [just] your opinion!" Corvino exemplifies the final sub-category of the 2nd bin with a statement like "God exists".

To give you a concrete example of a controversial case law (in the US), a statement about someone having "no status within the profession" was judged 6-5 to be a matter of opinion rather than a (false) factual statement. (No less than 3 separate standards for the distinction were offered by the Appellate judges.) SCOTUS denied certiorari, but two of the Supreme Justices felt like writing our their dissent nonetheless (which doesn't often happen in certiorari denied cases.)


Somewhat of an aside: according to (American philosopher) Norwood R. Hanson, statements of fact can never be false, only factual statements can be so. (But to me this sounds more like pedantry about language... I have no idea if other philosophers follow this prescription.)

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  • IANAL: Stating a wrong fact about someone in court isn't implicitly defamation. It's only defamation if you A] fully know it's false, and B] state the false fact with the intention to defame. Maybe you could get charged with perjury, though again, that generally requires intent to falsify or mislead. I think at worst, unwittingly stating a wrong fact in court (and getting corrected) will make you look bad and would hurt your case, but is not a crime in and of itself.
    – Abion47
    Jul 25 at 20:03
  • @Abion47 At least in the United States those rules only apply to statements about public figures or on matters of public importance. (I'm assuming you mean statements made out of court being judged in court. Statements made in court proceedings are generally absolutely privileged and cannot be defamatory as a matter of law.) Jul 26 at 2:49
  • @DavidSchwartz What if someone made a defamatory statement (i.e. fulfilled all the criteria of defamation) within a court proceeding, but the falsehood wasn't discovered until after the conclusion of the trial? Would that be a cause for a mistrial, a separate perjury case, a separate defamation case, or none/some/all of the above?
    – Abion47
    Jul 26 at 15:50
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    @Abion47 Most likely none of the above. If it met the criteria for perjury, then it could be charged as perjury. If the statement was made by an attorney (or knowingly solicited by one), it could be grounds for professional discipline. Jul 26 at 16:35
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Consider Hume's Fork.

A statement that falls on the analytical side of the fork is a fact. It is an analytical fact. Triangles have three sides. This is a statement that is true by definition. Statements of this kind would require us to doubt our own sanity in orde to doubt the statement.

A statement on the synthetic side of the fork is contingent on the particulars of reality. Such statements can be objective, or they can be opinion. Either of these can be true or false.

An objective statement would be one such as: drinking water is required for a human to live. This statement is subject to empirical verification. It is objectively true, since sad experience has shown that when a human cannot get water to drink they die.

Objective statements can be false. Example: It is not possible for humans to fly faster than the speed of sound.

A statement can be objectively true based on current evidence, but false in reality. Easy examples abound. "Powered human flight is impossible." This statement was true before powered flight methods were developed. Yet, powered flight is possible.

Opinion comes in flavors. (Of course, you see what I did there.)

One such is statements of preference. "The best kind of food is char-broiled steak." "American football is the best sport." "Luke Skywalker is the best Jedi."

Another type of opinion is a statement based on minimal or insufficient evidence. "This skull fragment is from a tyranosaur." A paleontologist may examine a fragment of skull and give his opinion that it is from a particular type of dinosaur. However, such opinion necessarily has a component of uncertainty. It should usually be expressed in a way that includes the uncertainty. For example: "I estimate that it is 90% likely this skull fragment is from a tyranosaur." Or another: "The DNA test gives a 99% chance that this man is not the father of this child."

The boundary between opinion and objective fact is not sharp. This is highlighted by the previous paragraph.

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    "A statement can be objectively true based on current evidence, but false in reality" - this seems like a strange and fringe definition of "objective". As per the more frequently used definition, objective truths would always be true in reality and not be dependent on a subject's (subjective) knowledge of evidence. The definition of "objective" you're using, I'd probably call "rational" instead.
    – NotThatGuy
    Jul 25 at 10:34
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    "Powered human flight is impossible" - to the extent that the truth value of this can change, it would be a temporal or conditional statement: powered human flight is impossible at the current time, or given the current level of technological development of humans. This would then remain objectively true if you update the time or condition appropriately (if "powered human flight is impossible right now" is true now, then "powered human flight was impossible 10 years ago" would be true 10 years from now). As for whether it's ever possible, that would be true from the beginning of time.
    – NotThatGuy
    Jul 25 at 10:55
  • There can also be this opinion: "I don't think powered human flight will every be possible."
    – Barmar
    Jul 25 at 14:20
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It depends on what school of epistemology you subscribe to.

If you follow Rene Descartes, you'll find that the only thing you can ever truly prove is your own existence. ("I think, therefore I am")

The most common view is that a fact is something with empirical evidence supporting it. E.g. "This book is long" is subjective; people perceive a book's length differently. "This book has 835 pages" would be fact; pages can be measured.

In this sense, a fact is only a fact if it can be completely measured and has no basis in subjectivity.

For a quick overview of many schools of epistemology, check this wiki page, it may help you narrow down what you're looking for here.

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  • Is it correct to say that "The temperature is 49.5°C" is a fact if only one person measured it?
    – AZeed
    Jul 26 at 0:57
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    The Kelvin system is based on the Boltzmann Constant and the Joule, which is in turn based on other, more specific things. Long story short, there is a perfectly standard way of measurement that doesn't differ depending on who measures it. Assuming they followed the standard method of measuring Celsius (basing it on the Kelvin measurement), then yes.
    – quixotic
    Jul 26 at 1:14
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    I think it is worth pointing out that you are asking for a bifurcation when in fact, if you will excuse the pun, it is more of a spectrum. Some opinions are more factual than others. "She is pretty" is a mix, since there are certainly objective measures of this, but it is ultimately subjective, and subject to the common standards of a society. And it is also very important to recognize that facts exist in a context. "I weigh 200lbs" might be fact here, but would not be a fact on the moon. "It is hot" may mean something quite different for a Canadian and an Algerian.
    – Fraser Orr
    Jul 26 at 1:29
  • You're right; facts do exist in a context. I'm no epistemics expert, but I'm not sure that some opinions can be more factual than others, as opinions are inherently not factual. Opinions can take into account more facts, but that does not make them more factual.
    – quixotic
    Jul 26 at 1:34
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I read that facts can be proven while opinions can't, but for example if I say: "It is hot!"

The statement "It is hot" is an opinion or a qualitative statement. The statement "It is 98.6° Farenheit" is a quantitative statement that can be established as fact since it can be independently verified with a thermometer. Whether 98.6° is hot, is a matter of opinion.

Another scenario is two people meet and swim in water that is 68°. The first person grew up swimming in the Pacific Northwest swimming in water that was 60°, the other grew up in Miami swimming in water that was 75°.

The water is 68° Person 1 says "Wow, this water is warm!" Person 2 says "Wow, this water is cold!"

Which information is fact?

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Hi if something is a fact it is to do with how it relates to the world separate from us. So facts and opinions are different concepts, opinions can be about facts but a fact is true anyway. Facts are to do with truth and truth is to do with the objective world.

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  • Agreed, but the question is, how do we know (in a particular case or generally) which is which - whether something is a fact or an opinion. More precisely, I suppose, whether a fact or a mere opinion is being stated.
    – Geoffrey Thomas
    Jul 25 at 7:06
  • Generally, the facts are the statements which are theorems in some formal system. Formal systems aren't part of the empirical world. Maybe this is not satisfying; I'm saying that 2 + 2 = 4 is a fact (in Peano arithmetic) and also that "all crows are black" is not a fact (since its evidence is empirical).
    – Corbin
    Jul 25 at 11:29
  • @GeoffreyThomas isn't that situation common? We just have to find evidence to support the propositions truth or falsity? Jul 31 at 13:18
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    Agreed, again. Then your answer is, I assume, that evidence differentiates facts (statements of fact) from opinions (statements of opinions). Best - Geoff
    – Geoffrey Thomas
    Jul 31 at 15:37
  • @GeoffreyThomas no I meant that evidence gives us reason to believe a proposition is true or false. Not that it distinguishes between facts and opinions, sorry if Im not too clear Jul 31 at 19:28
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You - and many answers - are assuming that "fact" and "opinion" are two distinct categories. They are not. One is not the opposite of the other and they are not exclusive. Most examples given here are overly simplified and don't do that justice.

In many longer discussions about what a "fact" actually is - such as this one - the word "opinion" never appears.

A fact is generally considered to be something "in the world", objective, measurable in some way, something for which a truth value can be established, at least in theory. Think "fact-checking".

Whereas an opinion is a mental state. A belief someone has about something. That belief can be identical to a fact. In a murder case, you can have an opinion about whether the accused is guilty or not. That opinion may or may not align with the facts (and we may or may not actually prove the facts).

Note that most everyday speech is shortened, with implied content that isn't spoken. When someone says "it is hot", the full statement, if you could convince them to state in full the meaning of it, would be something like "I feel that the temperature today is well above what I consider average." - and spelled out in full, this is getting close to something that could be factually checked. However, that isn't the difference. Many opinions could be fact-checked. What makes them opinions is that they are a personal, internal experience.

So you have the "fact" - part of the world - and the "opinion" - part of the subjective experience. About the first we can argue, observe, measure. About the second we cannot - that I disagree with your opinion is simply a different opinion, but there is nothing exclusive about it. Either, neither or both of our opinions could be true-to-facts as well, or be unknown or undeterminable with regards to that. A specific statement can be both fact and opinion. If the distinction is important, you need to make it explicit. Language being the murky thing it is doesn't always do that automatically.

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From a simplified philosophical perspective, science is what allows splitting what is objective (facts) from what is subjective (belief). Science is not only made by those people working at the CERN: you can do science at home. Read about the scientific method, and you will know how to do science. With time, it will be easier to determine if a judgement is a fact or an opinion.

Regarding the quotes, a person might sweat while other doesn't under the same conditions. So, "it's hot" is not easy to determine objectively, as a fact. You can propose a simplist solution:

  • A precise temperature, like 30.0 deg, is the starting point of "hot", (NOT strictly the best solution*, but can work most of the times).

* You risk falling into the Sorites Paradox: 29.999999...deg (nines till the infinite) will be cold, and 30.000000... deg will be hot, while they are exactly the same number!

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    The Kochen-Specker lemma (or more dramatically, the Free Will Theorem) ruins the assumption that empirical observations are derived from objective facts; not every property of a particle is objectively defined for all observers simultaneously.
    – Corbin
    Jul 25 at 11:30
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    @Corbin: right, and there's even more. While the OP and the answer address a simple ontological perspective, any judgement can be said to be composed of a subjective and an objective component (which fits your simple QM approach), while philosophically, the "objective" component tends to be totally dismissed. See George Berkeley: he proposes that there is no thing in itself, there is no matter; that all we can know is subjective. The pop lemma applicable here would be: "there is no spoon".
    – RodolfoAP
    Jul 26 at 6:00
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    The statement that science is what allows splitting facts from beliefs (i.e., scientism), is of course a statement that by itself cannot be scientifically proven. It is therefore not a fact that science is what allows splitting facts from beliefs, it is an opinion. Jul 26 at 12:46
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A fact is a statement proven to be true.

A statement proven to be false is a lie.

A statement of unknown truth value is a belief, a piece of fiction or a hypothesis.

An opinion has no truth value. An opinion is a moral or personal judgement about whether something is good or bad, right or wrong.

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    Doesn't a 'lie' require intent to deceive? If I make a false statement that I believe to be true, am I lying? Jul 24 at 7:42
  • That is not a lie, that is a belief which has an unknown truth value. A lie is known to be false. Jul 24 at 7:45
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    Yes. So, "A statement proven to be false is a lie", is false. Jul 24 at 7:48
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    I thought that you had perhaps unintentionally made a mistake and that you would want to remove it from your answer to avoid downvotes, that's all. Jul 24 at 8:09
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    It's not nitpicking. Accusing someone of lying is extremely serious and can have significant repercussions.
    – barbecue
    Jul 25 at 16:48
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"It is hot!" is an expression of experience, relative to (presumably) your own opinion of what counts as hot.

Hot according to whom? A person from the Arctic Circle spending time in summertime France may declare it's hot, but a person from the Sahara may disagree.

Meanwhile, I would dispute that a fact is a "proven" thing. It is merely an observed thing. And even then, it is observed by degrees and gradients according to what it is measured with. The word "proven" implies a standard of truth has been reached - for example, physicists may give a fact with an error margin or estimated certainty value.

Instead of saying it is hot, if you want to be factual, you may want to say how hot. So you say it's 30 degrees Celsius. This is better, but then still according to whose thermometer?

Similar for your sweating example - how much are you sweating in millilitre per hour? Is that a lot? What is a "normal" amount of sweat?

Any datum, whether fact or opinion, only has meaning when compared to, or in the context of another datum. A datum about ambient heat is compared either your opinion of what's too hot, or a thermometer value which presumably has been standardised in some way.

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Limiting us to people that accept logic as the only way to search for truth, and limiting again to sincere people, and limiting us to people that know and manage correctly logic laws, a fact is an opinion thought to be true, until demonstrated to be false. So e.g. classical mechanics was believed to be true, and fact until demonstrated to be false. So I would take the relative point of view, opinions that are considered with high probability to be true may be called facts until proven false. Low probability true facts are opinions. By that though, I may have two opposite opinions or more but not too opposite beliefs of facts ( I cannot believe at the same time with probability 99% 2 opposite facts unless there is doubt on them being opposite).

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There is a problem with the original statement. The statement is trying to making a logical, deductive proof. The problem is that the second sentence has taken one statement of fact and declared it to be the applicable to all cases without setting the proper local basis. Therefore, the validity of the conclusion is unknown under standard logic.

What that person did was this: If A is true, then B must be true. Therefore C is true. They need to establish why B logically follows from A and not just assert it. They also need to establish why C follows from B.

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This all comes down to your definitions. First of all, your definitions of the words "fact" and "opinion", of course. But then, also the intended meaning of the words in question.

For example, the words "it is hot!" can have quite a few interpretations:

  • It can state the fact that a machine is too hot to be touched.

  • It can state the fact that temperatures 40°C are uncomfortably high.

  • It can state the opinion that 25°C are uncomfortably high.

  • It can be irony spoken in the middle of a snow storm.

  • It can be a lie used to cover up the fact, that someone is impersonating somebody else in a hot country. All the while snowflakes are falling outside the impostors window...

  • It can state the fact that a part of cryogenic appliance is at room temperature.

  • ...

There are all kinds of shades of grey involved here, all of which come down to the precise intended meaning of the words. And that may not even be possible to deduce. Like when a poet deliberately uses ambiguity of meaning. In other contexts, words that are generally not precise may have a very well-defined meaning. For instance, when you hear talk of a cold magnet in some scientific context, it invariably means that the magnet in question is a superconducting magnet that needs to be cooled to cryogenic temperatures for operation. You may not have heard of this use of the word "cold" yet, but within the context, it has this exact meaning.

Only once you have established the intended meaning of the words, you may continue to analyze whether they are fact or opinion. And this is simple, in principle: Facts are opinions with evidence behind them. If you want to check whether an opinion is actually a fact, you must check the evidence. There is no other way. You can try to offload the burden of fact checking to other people whom you trust, but in the end, someone has to do the work. And other people's opinions are but hear-say evidence to you! So, when you do trust other people, do yourself a favor and make a mental note that you are trusting in hear-say.


This post contains the opinion of the author. Does it contain facts? This question is left as an exercise to the reader.

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If there was life on Mars two billion years ago, then the fact that there was such life is a fact, but is not known to us today to be a fact, but a scientist may be of the opinion that such life existed. So that is both a fact and an opinion. They are not mutually exclusive.

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  • 1 - Facts are relative I guess? 2 - Is fact vs opinion perhaps more like factual vs argumentative? Or positive vs normative? law.stackexchange.com/questions/1375/… then the scientist may make an objective claim...soooo a fact is not necessarily a 'true fact' ? idk i figured fact is actually an objective claim while an opinion is an actually a subjective claim...in your case re the life existed i think it's more of a guess or hypothesis or conjecture than an 'opinion' ? idk
    – BCLC
    Jul 25 at 21:23

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