Contrary to popular belief: knowledge, belief, and opinion are three completely different things.
The proper separation is Know, Do Not Know, and Opinion.
With every proposition, separate propositions with no truth-value(true or false value) from propositions with a truth-value, and then with propositions with a truth-value separate truth-values unknown from truth-values known.
Every proposition will fit into one of these three categories:
1) No truth-value exists.
2) The truth-value is unknown.
3) The truth-value is known.
A thing with no truth-value(1) is an opinion.
A thing with a truth-value unknown(2) is a belief.
A thing with a truth-value known(3) is knowledge.
Opinion
Every one is entitled to their opinions, as an opinion is neither true nor false.
eg: the waterfall is beautiful
eg: the waterfall is boring
As neither beautiful nor boring are attributes of the waterfall, both beautiful and boring are personal opinion.
Do Not Know
Every belief is justified relative to an individuals education and mental health status, from which it follows that an individual lacking an education in a certain matter, or one with a mental health disorder, may hold irrational beliefs in a matter.
It is impossible for any single individual to know everything, which is why every individual has their own list of things they know and do not know.
An individuals measure of belief about a thing they Do Not Know is dictated by probability, therefore it has nothing whatsoever to do with accepting a thing as true or false.
Things I do not know:
eg: if aliens exist or not.
eg: if the lochness monster exists or not.
eg: if bigfoot exists or not.
I do not know if aliens exist or not. I have knowledge of a multitude of life forms here on earth. I have knowledge of the vastness of the universe. From this the existence of aliens can be said to be highly probable.
I do not know if the lochness monster or bigfoot exists or not. I have knowledge of people saying they're witnesses. I have knowledge of people found to have created hoaxes. From this the existence of both the lochness monster and bigfoot can be said to be low on the probability scale.
Know
Every individual knows a thing no other individual knows nor can know. There are things known by an individual others can also know. There are things every individual should know.
Things only I know:
eg: what time my clock displayed when I looked at it this morning when I awoke.
eg: what time my clock displayed when I turned my coffee pot on to make coffee.
Things I know that others can know:
eg: my home address.
eg: my approximate height.
Things every individual should know:
eg: no single truth contradicts any other truth.
eg: every truth is singular.
eg: no word has an inherent meaning.
The Lists From This Page
No Truth-Value (Opinion)
The waterfall is beautiful.
The waterfall is boring.
With a Truth-Value
Do Not Know (Belief)
If aliens exist: high probability.
If the lochness monster exists: low probability.
If bigfoot exists: low probability.
Know (Knowledge)
What time my clock displayed when I looked at it this morning when I awoke.
What time my clock displayed when I turned my coffee pot on to make coffee.
My home address.
My approximate height.
No single truth contradicts any other truth.
Every truth is singular.
No word has an inherent meaning.
From here you continue to populate your lists and keep them up to date continually.
Conclusions
It is irrational to assert a thing with a truth-value to be an opinion.
It is irrational to assert to know a thing you do not know.
It is irrational to assert belief means accepting something as true, as ones measure of belief is probabilistic which is [0-1] non-inclusive.
It is wise to properly separate things you Know, things you Do Not Know, and Opinion. It is the fool that mixes them.