I am having trouble precisely telling the difference between a fact and an opinion. For example, let's say there is a man that weighs 500 pounds. Would it be a fact to refer to him as fat because that could proven. Another example would be saying Donald Trump is a bad president. Could that proven or would that just be an opinion?

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    "to prove" is a thorny issue... For the frist case, we have to rely on the def of "fat person" (not so easy) while for the second one we have to rely on the def of "good/bad person" (much more difficult). – Mauro ALLEGRANZA Sep 4 '17 at 7:44
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    Both of the examples you gave depend on definitions, meaning if you have a very precise definition of the predicate "fat" or "a bad president" then you could look at the object and figure out whether or not it hits all of the criteria necessary. The issue that comes into play around that point is vagueness, what is the cut off between not fat and fat? What is the cut off between bad and just okay? That SEP article I linked to covers the problems with delineation and vagueness in issues like this. The problem is that facts cannot be contested. – Not_Here Sep 5 '17 at 10:35
  • I'd argue both are opinions, but, if you said obese, that would be a fact, because obese has a medically specific definition. Ultimately, the question is: is the adjective well-defined (Donald Trump is a millionaire) or do people define it on their own (Donald Trump is rich). – user935 Sep 9 '17 at 2:29
  • Not really a question for this site. It is a fact that a man weighs 500 pounds. It is an opinion as to whether he is fat or not. – Swami Vishwananda Sep 14 '17 at 4:56
  • There are good reasons to think that the fact/opinion distinction is not clean, clear, or useful. It may foster further confusion. See arguments here: philosophersmag.com/essays/26-the-fact-opinion-distinction – ChristopherE Oct 27 '17 at 11:23

This may sound bewildering but everything we can say is an opinion at best.

  1. Definitions are purely opinion based. "There are nine planets in the solar system" appears to be a fact, except that the word planet implicitly assumes a definition just like fat does in your example.

    "There is a man that weights 500 pounds" implicitly assumes the definitions of its constituent words are well-known. Nevertheless, well-known definitions are definitions, which are opinion based.

  2. Every proposition that is either true or false involves judgement; every judgement is an opinion.

  3. We can say something about the fact, but what we utter are seldom the facts we are referring to; we can speak truth but we rarely speak the fact.

    Paris is a fact; everything we can say about Paris are opinions. Paris and what we say about Paris are never one and the same.

  4. Everything we know about the world is inferred from our sensations, i.e. the ultimate source of our knowledge is the mind. We believe the causal origins of our sensations are in the physical world, but this belief is a leap of faith, and, if there is any reason for believing it true, that reason is also based on sensations.

    You see a red apple and you firmly believe that that apple is red. Someone else sees the same apple and firmly believes it is yellow. It is possible that both are speaking the truth because colour is a mental event, not an intrinsic property of the apple. It is possible that the same apple which causes red sensation in your head causes yellow sensation in the other person’s head.

    As Einstein has pointed out, even such "objective" qualities as mass, length and duration, which used to be thought as intrinsic properties of the objective world, are not independent from the observers.

Naïve realism leads to physics, and physics, if true, show that naïve realism is false. --Bertrand Russell

Source: Einstein. Ideas and Opinions

This piece of pedantry explains why freedom of speech is important in the pursuit of truth.

Source: Knowledge by Acquaintance And Knowledge by Description

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    Downvoted because: (1) doesn't make any sense. First, it's not clear in what sense 'definitions are opinion based'. Words have definitions - nobody is going to deny that. Why does that entail that statements that involve words - which have definitions! - can't express facts? (2) is just false. Standard contemporary accounts of propositions hold that they are mind-independent entities. So it's not true that every proposition involves judgement. Continued... – possibleWorld Sep 16 '17 at 16:13
  • ... (3) starts off well, but goes off the rails. Paris isn't a fact; it's a city. And all of the stuff about direct/indirect realism is completely orthogonal to the OP's question. Surely you realize that we can grasp the opinion/fact distinction without believing that "everything we know about the world is inferred from our sensations," right? Also, the bit about freedom of speech is a non-sequitur. – possibleWorld Sep 16 '17 at 16:18
  • Propositions express mental states, not the fact this mental state reflects. The mind is a mirror; propositions express the mirror image, not the object that causes this image. – George Chen Sep 16 '17 at 17:30
  • Standard contemporary accounts are mostly bull. The fact that someone uses this argument reflect the sorry state of standard education. – George Chen Sep 16 '17 at 17:32
  • (3) is important. The ultimate source of human knowledge are sensations, i.e. mental events, not the outside world. Those who failed to understand this have accused Russell of being an idealist. – George Chen Sep 16 '17 at 17:33

I'd suggest that a proposition like your "this man is fat" can only be a "fact" if it's operationally verifiable, as per, e.g., https://plato.stanford.edu/entries/operationalism/ and https://en.wikipedia.org/wiki/Verificationism

So first you'd have to define "fat" as, say, "ratio of weight-in-pounds divided by height-in-feet greater than 35". And then you'd have to specify the construction of "experimental apparatus" like scales and rulers for your weight and height measurements.

And now your statement, "this man is fat", is a true-or-false fact, at least with respect to your verifiable definition and measurement procedure. Of course, somebody else can come along and suggest that bmi (body mass index) is a better definition of "fat" to begin with, whereby your whole definition is just an opinion.

But now you simply need two different words, like "bmi_fat" and "height/weight_fat", to distinguish your meanings. And those words ultimately just refer back to your different bmi and height/weight measurement procedures. So a statement can only be a fact if it's accompanied by an operational procedure that unambiguously determines whether it's true or false.

And I suppose you could try introducing "good/bad" definitions and measurements for Trump, too, but you'd probably run into people suggesting lots more alternatives than for "fat". And then it becomes a matter of opinion which definition/procedure to use. Until that's specified, "good/bad"'s just an opinion; but once it's specified, "good/bad"'s an operationally verifiable fact.

  • Is your answer is implying that facts are socially constructed from language? Does this mean that provided the "correct" language is specified, everything could become a fact? Say I think you are dumb, which I define as a person having less than 500 reputation in Philosophy SE (me included hehe). Then, me saying "John Forkosh is dumb" becomes a fact under my world view, not an opinion. I feel this is too simple. I think facts are related to reality, not to socially constructed language-based definitions. – luchonacho Sep 16 '17 at 7:23
  • @luchonacho Sure, if you're >>defining<< the word "dumb" that way, then you and I are dumb (but you're a little dumber than I am, hehe:). But I wouldn't call that "socially constructed". It's formalism, mapping syntax to semantics, whereas "social" has connotations that are incorrect in this situation. But I guess you might try arguing that mathematics is "socially constructed", in which case this would be pretty much the same kind of thing. – user19423 Sep 17 '17 at 8:05

Quoting Plato, "opinions are blind things" and they are bound to change as time goes on , facts are different in that regard , that they remain unchanged or get added/modified at best(in theory). Mathematical facts are the best examples , as the existence of numbers for example can be considered as an unwavering fact or at least the best we can claim to be so. We can always ask the question whether numbers really exist or just are a figment of our imagination or if its a necessary abstract and so on , in fact in mathematics many paradoxes and any such questions led to the refinement of it but never really to the dissolvement. This is the key attribute of facts, that they do not dissolve in itself when questioned and are refined and added on but stands by itself as a pillar to trust on.

The same way it can be asked whether your people weighing 500 pounds are fat statement may be established as such but to be considered as a fact or even resembling it , it should be able to stand on its own and be able to withstand counter arguments as well containing many defending ones. Such as , would a person still be considered fat if he were to live in a society where 600 pounds is the average or what if he only has 5 % body fat and the rest are muscle? The claim is then easily deconstructed , because the statement is in itself lacking in detail or in correct general formulation. So to say it is a fact is in this example not very possible unless you elaborate on your statement.

IF you were to state but for example being fat is dependable on time and environment , then you have something more resembling a fact then an opinion because europeans oftenly appear much fatter in for example Indonesia, where the average weight is much lesser. So it seems pretty solid in its empirical validity but when you ask the question , what of people who shorten their own life by eating fatty and pretty much weigh 500 pounds. Does it matter where they live or what the average is , if the fattening in appearance also means harming himself in health , should that person not be considered fat as well , as the adjective implies a negativity in itself independently of where one lives? So the argument is strong in one area , that of societal but still can be attacked from an individual, linguistic point of view.

As you can see it is hard to determine a fact but you can certainly can say that one statement is truer than the other. The same way you can see facts and opinions, if an opinion is the most arbitrary thing you can state a fact is the truest one that can be seen as a theoretical pillar. And since one opinion can be truer or more resilient than the other , it is fair to say between those two you will find a continuum.


There can be disagreement about the facts. Vague terms like "fat" are often a problem. But we also have a situation now where various authorities are claiming different sets of facts about various states of affairs. In that case, we need to examine the evidence and carefully scrutinize the sources of information. This is becoming increasingly difficult because we used to rely on things like photographs and videos, but now they can be so easily realistically altered or created that we cannot rely on digital images as strong evidence for things that are happening or have happened.

We have a president who has repeatedly demonstrated that he is loose with the facts. He, like many other politicians, makes up facts on the spot or seems to give misleading information intentionally. In that case, we would have to be more careful about trusting those sources for facts because they have a history of being unreliable. And increasingly, the facts given by other sources are often skewed or presented in an apparently biased way that people often do not trust those sources anymore either. So there is some level of judgment that takes place about accepting various facts from other sources. It requires some level of trust in the source. Some people believe the president is great, and others hate him. They don't agree about whether he is a "good" president or agree on a definition. Those are opinions.

Facts are perhaps statements about states of affairs in the world that have some sort of widespread mutual or definitive agreement or measure, but they can still have some level of uncertainty attached to them and can require some additional assumptions to believe. I know whether I feel hungry or not, or whether I feel hot or cold. Those are facts from my personal experience for which I have very little or not any doubt. I am using the words to describe my experience. You do not have access to what I am feeling to know whether it is true or not. You just have to take my word for it. I can lie, so there is some level of uncertainty from your point of view. But to say that it is hot, meaning something that applies to everyone, would be an opinion up to a certain point depending on how we define it. We might agree on the measurement of the thermometer, but disagree about whether it is hot.

If I were going to make a statement that I thought would apply to the experience of everyone in my environment, then I would be asserting a fact (e.g., it is raining outside my window). I could be hallucinating or lying, so there is always some level of uncertainty attached to statements that would apply to the experience of others in the environment or beliefs about the environment outside of my experience. Counting the number of characters in this string of words and be reporting it would be reporting or asserting a fact. There could be an error in the character count, but we have reliable ways of checking that we trust. A judgment about whether it is too long or not would be your opinion. :)


Fact is something that is universally accepted as true. You are not supposed to proof it. They serve as a base from which you start to deduce things. [Like Axioms].

Opinions are much more inclined to one's perception. You are either judging or accusing or giving your view of things. Obviously, you have to come up with good justification.

  • Universally accepted? By whom? And what if there is no agreement? – Logikal Oct 26 '17 at 18:05

Where i come from the term "fact" expresses that a claim "must be true". That is a fact cannot be wrong. The word is analytical. You can not get facts wrong. You can make a false claim that you believed to be true. The claim all swans are white is false precisely because non white swans (black swans) were discovered later on . A triangle cant have 2 sides for the same reason facts cannot be false or wrong. What you have is a persin who is just wrong about the claim. They are using the wrong term.

For me to claim x is a fact and get the answer wrong means x was false and i made a mistake. Its like an indirect proof. I claim x and someone points out there is a not x instance doesnt it mean i can deny the original proposition? How can anyone believe facts can be wrong and the person is correct? Where is the reasoning behind that conclusion?

Facts must be true by definition and facts also never change value. Emotional people will intensionally leave out specific details in a circumstance to express trurh values can change. The way to combat that is to be excessively be detail specific. Now sone will say this is excessive but will show that at the time and place of occurrence the result of x will not change ever. Your birthday is a fact. It will never change.


A proposition is anything that can be true or false. For example, it is true or false that the earth is spherical. We know what 'earth' and 'spherical' mean, if you have a different opinion on what they mean than the generally accepted definitions, then you do not have a mastery of the English language and cannot meaningfully counter. A proposition is true or false because it claims (or 'proposes') that world is a certain way which it either is or isn't. If the world is that way, then the proposition is true and is a fact.


The man weighs 500 pounds. That's a fact.

The man is fat. That's an opinion, although coming close to a common definition.

Facts can be proved by experts in the respective field with (almost) always the same result. Facts always remain the same.

Opinions can be differing. They can change from person to person or even from time to time. Here is an example:

When I was young, I knew a lot of elder persons in Germany whom I considered fat. When I visited the USA for the first time, I saw a lot of persons whom I considered really as fat as I never had seen before. I remember a sheriff ordering a Coca Cola and pouring a pound or so of sugar into the drink. After that the people in Germany appeared no longer fat to me. (Alas meanwhile the Germans have caught up.)

  • if "fat" can be equated to "obese" as a definition, then it's not just opinion that a 500 pound human is fat. there are objective medical standards to the meaning of "obese" and a 500 pound human will certainly satisfy those standards. – robert bristow-johnson Sep 15 '17 at 7:31
  • Of course, if there is such a definition fixed, then it is fact that the 500-pounds-man is obese. – Heinrich Sep 15 '17 at 12:57
  • 'being fat' and 'being 500 pounds' are both properties. They differ in that to attribute fatness to an object typically requires some sort of reference class, whereas attributing 500-poundedness does not. But that doesn't mean that 'the man is fat' is opinion whereas 'the man weighs 500 pounds' is fact. Both expressions can express facts. – possibleWorld Sep 16 '17 at 16:09

if i think it, it's a fact.

if you think it, it's an opinion.

don't believe everything you think.

  • and Trump is a horrible president because he is a horrible alleged human being by any measure. the sooner he's removed from power by any means the better for the planet. – robert bristow-johnson Sep 15 '17 at 7:25
  • This answer might capture some ordinary uses of 'fact' and 'opinion', but it doesn't at all capture how contemporary philosophers use 'fact' and 'opinion'. – possibleWorld Sep 16 '17 at 16:05

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