I think this is really a question of semantics, I meant simply that they imply different things, but let's do some semantics, shall we? Here's how I would define the four things.
Truth: This is an abstract notion, mainly I agree with how Plato defined it, as the ultimate reality. It is not whether or not something specific is "true" but rather, the abstract notion of truth.
Reality: This is what we experience in our day to day lives. It's a collective sensory experience because we generally perceive the same things in our day to day lives, as human beings. This concerns experience. It is what we experience in a general sense, not anything specific to be experienced.
Fact: This is what has been proven to be real (notice I didn't say "true"), through evidence and reason. A fact is a specific occurence, or segment of what I more broadly call reality. In other words, it is an event that can be experienced, whereas reality is the whole extent of events that can be experienced.
Opinion: This basically when you say green is the best color or that industrial music is better than techno: there is nothing objective about opinion, I would define opinion as an expression of preference.
Again, that is how, philosophically I would define these things, but I think there are more interesting things to be pondered and solved, from the standpoint of philosophy, than semantics, since everyone might define these terms a bit differently.
Via Typh0n wrote, (1) "Truth: This..an abstract notion...I agree with how Plato defined it, as the ultimate reality."
I happen to like Plato's allegory of the cave. We as a species can not see the whole truth. We can only see slivers and angles ot truth and reality based on our limited perceptions. Truth is always unfolding before us as more and more data is discovered by science. What many view as truth is merely perceptions and opinions. For one to say, "I think, feel or believe this to be true," is in fact employing emotional reasoning. I feel it, ergo it is the truth.
This irrespective of your belief having not been proven by science and science methodology. Even in science we start with a hypothesis and take it for granted as truth. Only with new discoveries do we find the error of our ways. It is a main reason I favor science over religion. Science grows over time as new developments arise. Religion stipulates original hypothesis to explain the natural order of things and is inflexible in changing its belief despite overwhelming evidence in contrast.
(2) "Reality: This is what we experience in our day to day lives. It's a collective sensory experience because we generally perceive the same things in our day to day lives, as human beings.
This is experiential learning. We are a product of the nature and nurture paradigm. It is life's experiences, provided we are open minded and amiable enough to learning new lessons through insight and reflection, that we can grow. We expand our understanding of ourselves, others and the reality we live in.
(3) "Fact: This is what has been proven to be real (notice I didn't say "true"), through evidence and reason." and "...fact is ... what I more broadly call reality."
I concur. To me the only reliable truths are not opinions or beliefs but hard objective facts proven and replicated by science.
(4) "Opinion...there is nothing objective about opinion..."
I again concur. Alas wars are fought over ideological beliefs. They are in a metaphorical and philosophical sense illusions. We believe in certain things not substantiated by science and are prepared to go to war over what amounts to differences of opinion in the form of beliefs. We delude ourselves in doing so.
