I can’t even count the number of times that students have said, “That is just an opinion,” in my philosophy classes over the years. I realize that students have been taught in the K-12 system that there is a distinction between facts and opinions. Unfortunately, this distinction is largely meaningless. It doesn’t tell us anything important. Opinions are beliefs and some beliefs are about facts. So, stating that something is an opinion does not tell us whether it is factual or not.
I’ve found that this distinction, as used by students, is usually about the difference between a statement concerning an objective matter or a statement about a preference. But as such, it is really a distinction between something that is objective and something that is subjective. For instance it is my opinion that 2 + 2 is 4 and it is also my opinion that mint chocolate chip ice cream is awesome. They are both opinions but one is about something objective and the other about something subjective. Whether a certain flavor of ice cream tastes good is mostly relative to a particular subject, but whether 2 + 2 is 4 is not relative to a subject. It is objectively true. The important distinction here is not between facts and opinions; the important distinction is between objectivity and subjectivity.
Here are some articles on this topic.
1) “The Fact/Opinion Distinction” by John Corvino in the Philosopher’s Magazine online (TPM Online)
[This article criticizes the distinction in more depth than I did above, but the criticism is along the same lines as mine.]
2) Justin P. McBrayer, “Why Our Children Don’t Think There Are Moral Facts” in the New York Times, The Stone blog
[This article both criticizes the distinction and advances some claims about moral education. I don’t think that the claims about moral education are well-supported.]
3) Mark Buchanan, “Common Core and Common Values” in Bloomberg View
[This article defends the distinction on the grounds that it improves moral education. I think that this article is deeply flawed in approach to both logic and ethical theory.]