What is the difference between opinion and fact?

Question

This is a usage question. Seriously.

Folks use both words with great confidence, which leads me to believe they know what they're talking about.

We are assured that on EL&U questions must not be posted whose answers can only be opinion-based. And - if your answer isn't factual, it'll be closed immediately. Yes. We know the drill.

So it came to me as a shock today when someone with a rep of more than 50K (a fellow whom I like, incidentally) began answering a question with "I think ..."

Personally I have nothing against it. Opinions are superior to facts - in Decartes' ... opinion ... anyway. The word opinion is a derivative of the word opine, which means "to think" in Latin. Had Decartes thought ... damn it ! ... had he thought it was the other way around, he would have said "I've got some facts here, therefore ..." But he didn't.

According to the standard definition, a fact is something that can be proven right. (They usually leave it at that; however, an honest person should hasten to add " ... or wrong").

An opinion is something that cannot be proven right, nor wrong for that matter.

Or so they say.

A long, long time ago scientists took it as a matter of course that the Earth was the center of the Universe. To them and their groupies this was a fact. At the same time other scientists protested that the Sun, and not the Earth, was in the center, or slightly off-center. The two schools of thought continued to prove their rivals wrong and their own theory right. This went on for many centuries. Geocentric, heliocentric.

(There was, to be sure, Nicholas of Cusa, who explained that the Universe as we know it cannot have a geometrical center, but he was pointedly ignored).

Then, many centuries later, someone demonstrated, or thought he did, that neither the Sun nor the Earth were in the middle. Today's scientists believe in the almighty singularity that appeared out of nowhere and detonated itself with such vim and vigor that space, time, matter and energy suddenly appeared and began rapidly to expand in all directions centerlessly. That is now a fact, while the older ideas are no longer viewed as facts: they're outdated opinions. (Facts cannot be outdated: facts are forever, as Cleopatra used to say).

"What is the source of this?" demands the skeptical Mr. X squeamishly when he encounters information that doesn't quite fit into his well-adjusted outlook.

The ancient Romans thought the story of Troy was fiction. Troy? Fiction. Of course. It's a fact. Only ignorant people believe it might be true.

Folks continued to hold this ... op ... whoa. Folks continued to view the fictional nature of Troy as a fact until someone somewhere developed a different ... opinion ... damn it ... Eventually, an amateur named Schliemann dug up something that definitely wasn't Troy. Then, reluctantly, some folks began to agree that it was ... well ... kind of ... Troy.

Now we know for a fact that the Trojan War took place sometime in the 12th Century B.C. Look it up if you don't believe me. What's my source? I've got many. Wikipedia is one. Britannica Encyclopedia is another. There are countless books and essays.

Yes, but all those encyclopedia entries, all those textbook chapters - they didn't just magically appear, did they? No. They were written by, well, people. Reputable and scholarly, but still human. What was their source? Evidence? What evidence? Homer and Schliemann?

But no one questions Troy anymore. There's just no need. Too many entries. Too many books, well-indexed and cross-referenced. Consensus. Part of the paradigm.

But. Someone was first. The pioneer. The trailblazer. The idea's only champion at the time. At some point in the past that someone said, "Homer's account was based on actual historical events."

They called him a moron and told him to keep his uninteresting opinions to himself. Until ...

As it turns out, a fact is an opinion agreed on by many. Evidence or no evidence. An opinion is a unit of information someone believes in. A fact is a unit of information many reputable people believe in.

When you're stating a fact, it does help if your ... uh ... "source" ... is "reputable," i.e. the person whose essay or book you're so cavalierly alluding to is properly certified (has the stamp of approval, a.k.a. "the Sign of the Beast").

Am I right? ...

Now comes the comical part. I'm pretty sure a whole bunch of folks will want to close this question because "it is primarily opinion-based." Which is to say that, while we only consider facts, and never opinions, here on EL&U, what a fact or an opinion actually is is a matter of opinion, not fact.

Or not.

If not, please give me your definition of those two words.

Answer 1

From the following snippets of your question:

• We are assured that on EL&U questions must not be posted whose answers can only be opinion-based;
• it came to me as a shock today when someone with a rep of more than 50K ... began answering a question with "I think ..."; and
• while we only consider facts, and never opinions, here on EL&U, what a fact or an opinion actually is is a matter of opinion, not fact.

I take it that you're questioning the difference between fact and opinion in the context of EL&U.

Since subjective questions are not ruled out completely, it is safe to say that answers need not be restricted to those that are lab-provable or maths-derived.

From the same link, the primary qualification is:

• insist that opinion be backed up with facts and references

so we should consider the terms fact and opinion in relation to EL&U posts to be synonyms of substantiated posts and unsubstantiated posts.

It's interesting to note that some unsubstantiated answers are tolerated while others aren't. Personal experience is certainly a source of substantiation, but it can also be really hard for others to verify, particularly posts that reduce to 'Trust me, I know what I'm talking about'. As you point out, there is a whole spectrum between fact and bare opinion, so where should the line be drawn? To answer this, we need to return to the purpose of this site.

The stated aim is to build a library of detailed answers to every question about English language and usage. The site goes on to say how questions should be answered:

Read the question carefully. What, specifically, is the question asking for? Make sure your answer provides that – or a viable alternative. The answer can be “don’t do that”, but it should also include “try this instead”. Any answer that gets the asker going in the right direction is helpful, but do try to mention any limitations, assumptions or simplifications in your answer. Brevity is acceptable, but fuller explanations are better.

In other words, it's not whether an answer is categorised as opinion or fact. Rather, the standard is that the answer has to be useful. Lone opinions that have no supporting documentation and no logical argument fail this standard, but opinions that are supported should be well received.

Answer 2

A long, long time ago scientists took it as a matter of course that the Earth was the center of the Universe. To them and their groupies this was a fact. At the same time other scientists protested that the Sun, and not the Earth, was in the center, or slightly off-center. The two schools of thought continued to prove their rivals wrong and their own theory right. This went on for many centuries. Geocentric, heliocentric.

(There was, to be sure, Nicholas of Cusa, who explained that the Universe as we know it cannot have a geometrical center, but he was pointedly ignored).

Then, many centuries later, someone demonstrated, or thought he did, that neither the Sun nor the Earth were in the middle. Today's scientists believe in the almighty singularity that appeared out of nowhere and detonated itself with such vim and vigor that space, time, matter and energy suddenly appeared and began rapidly to expand in all directions centerlessly. That is now a fact, while the older ideas are no longer viewed as facts: they're outdated opinions.

This what you describe here are neither facts, nor opinions but theories.

Answer 3

BBC has this article on Fact or Opinion that explains the difference very well and I find it useful in explaining what primarily-opinion-based means on ELU:

A fact is something that can be checked and backed up with evidence, e.g. In 2010, Lionel Messi was named FIFA World Footballer of The Year. We can check these details by looking at FIFA records. Facts are often used in conjunction with research and study...

An opinion is based on a belief or view. It is not based on evidence that can be checked e.g. Wayne Rooney is the best football player in the EPL. Some people might think there are other players in the EPL who are better than Wayne Rooney...

Regarding questions that can generate primarily-opinion-based (POB) answers, I think it is a good guideline to close those questions as they could be only useful to the OP him/herself and it might not be a good reference to current and future readers. I believe the motto on Stack Exchange in relation to asking questions is "Ask questions that can benefit others and don't ask questions that can benefit only yourself." Majority of POB questions are beneficial only to the OP and it is not good for the community. Some of questions closed as POB are:

1. Punctuation questions: There is no unified rule on punctuation in English, so many of them could generate only POB answers depending on posters' style and preference (style book).

2. Why is it? or Which is better (or best)? type of questions: It doesn't work very well on ELU. However, some of them are well-received when users could find them answerable with reference and research.

3. What do you think about it? type of question. Unless they are about regional differences or nuances, they are not well-received.

As I commented above, 5 votes are required to close any question and I believe it needs more than 5 votes to delete an answer depending on your rep points (I can only recommend deletion at my reputation). Opinions could be different, but facts could not. Many grammatical points are opinion-based and sometimes different depending on authors, but they can be reasonably understood by English speakers. There is a grey area between an opinion and a fact. But the important thing is the guidelines of ELU doesn't encourage a question that could generate only POB answers.

I think the linked questions on Meta, What the “primarily opinion-based” close reason is for, Why is question 146045 opinion-based? and What is wrong with “Opinion-Based”? would be interesting for you. There are many more if you use the search.

I agree with @Lawrence. Answers should be as correct—hopefully more fact-based than opinion-based—and useful as possible to current and future users.