"a personal belief or judgment that is not founded on proof or certainty"
"a view or judgment formed about something, not necessarily based on fact or knowledge"
The problem is the vagueness.
These definitions do a good job of describing what qualifies to be called an "opinion", basically summing up the two notions I was talking about in one convenient package.
Subjective opinion, or taste
A basic aesthetic appraisal of something, like a sunset (hate to use clichés here, but who cares) being "beautiful", is not founded on proof or certainty.
But it also isn't founded on ANY kind of rational or logical considerations at all - neither does it actually make any factual statement about the object in question.
It makes a statement about the mental state in reaction to the object.
The sunset isn't beautiful - the observer's brain perceives it as beautiful. If there's any objective ambition in a statement like "this sunset IS beautiful", it really means "it will appear beautiful to others, too, because we all share similar brains".
An aesthetic judgment of some complex art work, may involve all kinds of rational thought, determining which elements work together in what way in order to create some aesthetic effect, if you look at it one way or the other, etc.
But it'll still be founded on aesthetic perception, i.e. a subjective mental state.
Factual opinion (not an official term, just something I thought fits)
Now, some kind of "this country is going to the dogs, and here's apparently why", is also a "judgement not founded on proof or certainty".
But it actually TRIES to make a claim about supposed facts. The facts ARE out there (unlike the beauty of the sunset, which is all in the mind), but impossible to determine with "proof and certainy", so you go by what you have.
Should proof and certainty for this opinion crop up, it'll become factual knowledge.
Should some appear that debunk it, it'll CHANGE and become factual knowledge then.
This type of opinion is an attempt to approach factual knowledge. Which means, it can be more accurate, or less accurate, than another.
If your judgement is based on faulty logic, it can be debunked, or attacked.
If the logic is so awful beyond remedy, this opinion can be simply indisputably wrong.
For the other, no proof will, or can ever crop up. And neither can any logic begin to rebuke it. There is nothing to prove, or debunk - it's a first-person observation about one's own mental state, and nothing else.
Confusing subjective opinion with factual opinion
So if you find a sunset beautiful, but insist that it actually IS beautiful, and it's not just you and some other people... you confuse your mental state with fact, or factual opinion.
If you have some political views about something, but get overly defensive about people criticizing it, saying "it's just an opinion, and I have a right"... you confuse your judgment of actual facts, with a subjective sentiment.
Opinions themselves as facts
The fact that a given person has an opinion of any kind, is a fact in itself.
However, the subjective opinion, is an observation of this "fact" itself. It is based on the KNOWLEDGE of one's own mind.
(Paradoxically, it can also be an opinion of it, as what one thinks of one's one emotions, or views, isn't necessarily complete, or accurate - but that's waay to out there right now.)
The factual opinion may be phrased as an observation about this "fact", like "I think that X", but its CONTENT still refers to some given external circumstance that exist independently of the observer.
Another way to break it down:
Knowledge vs. Value
If we say that there are two basic departments in our mind in relation to the world:
-Knowledge - dedicated to creating an image of the external world inside the mind. Can be directly compared to the external world.
-Values - dedicated to deciding what is "good" or "bad", what is "right" (not "correct"), and what "ought" to be. Is one's personal relation to the external world.
(There's also the department that can create imaginary scenarios, but that plays its function in both of those.)
... then the subjective opinion would be a value statement, as in "I value this sunset for its beauty", or "I value this funny face for its hilarity", and the factual would be in the first department.
Fun with Words
So what exactly am I supposed to take from a description like this:
not necessarily based on fact or knowledge
So if it MAY be based on fact and knowledge, it wouldn't be an opinion anymore, would it?
Or is it really BASED on knowing certain facts, but is an opinion by the virtue of putting them in an unprovable construct?
Well, in one case, the "fact" would be one's own value / mental state, in the other, it would be an external circumstance that may or may not correspond.
However, in the first case, there is no external fact at all, so it's not based on it?
It's as comprehensive a definition, as it's almost useless.
All three of these are saying the same thing, the statement may be factual, but there isn't sufficient evidence to support it (thus it isn't founded on proof or certainty, or in other words, it isn't necessarily based on fact or knowledge).
Or in your second definition it is a "subjective mental state", which again is saying nothing contrary to or different from "a personal belief or judgment that is not founded on proof or certainty" or "a view or judgment formed about something, not necessarily based on fact or knowledge"
And therein lies the problem
"The second definition again doesn't contradict the Oxford definition."
Well, it doesn't contradict it. It specifies it.
The vague Oxford definition includes both meanings in its wording, and both of my different definitions specify the actual two different notions contained within it.
Neither "spider", nor "horse", contradict "animal".
But they are still two completely different species.
Both your definitions are encompassed under the single definition from the first two sources.
Exactly!
As I said, it's the right way to give a brief definition of what passes for an "opinion" - but I've shown at the beginning how these two different notions can fit into Oxford's wording, and yet can it be argued by anybody that distinguishing between the two isn't important when it comes to actual judgment and discussion?
I'd say it is, as described in my "confusing the stuff things" segment.
The only other meaning of the word "opinion" would be in the sense of "legal opinion" or "medical opinion" etc., but you never claimed those meanings as your reason for being so confused about what meaning of the word we were trying to use.
Well, this one sums it up rather well:
http://dictionary.reference.com/browse/opinion
;)
The 3rd one is more of a sub-group of 1., though, if you think about it.
A medical opinion is aimed at facts, but obviously hasn't quit gotten there (you won't have to ask a pysicist for a second opinion on the speed of light, for instance).
Though, I guess, there may also be some value judgements involved, concerning ethical considerations, or what alternative would be "better" for a client, etc. - but I don't know that much about those areas :)