As a science teacher I always have a lesson or two near the beginning of my 8th grade science course on the difference between fact and opinion. On one of my guided practice handouts, for example, I might list several pieces of information and ask the students to write whether or not each represents a fact or an opinion. A sample list might include:
A clear sky usually appears blue.
A blue sky is very pleasant to look at.
The rosebush has thorns.
Carbon is an element.
The girl in the picture is very pretty.
Science is easier than math.
Most adults can easily pick out the facts in this list. Items one, three, and four are facts; the others might apply to you but not necessarily to everyone else. Therefore, they represent opinions. But I could have added a third possibility to the mix. I could have asked them to choose among fact, opinion, and belief. I could have added items to the list such as:
God exists as Father, Son, and Holy Spirit.
Jesus died on the cross and was resurrected to save the souls of mankind.
Every word of the bible is true.
Allah is the one true god,
Mohammad was the highest prophet.
Every word of the Koran is true.
If I asked them to choose among fact, opinion, or belief, most people, including my students, would be honest enough to label those last examples as beliefs, even fundamentalists. But what if I left out the belief part and forced you to pick between only fact and opinion? Those should be the only two choices anyway; adding belief to the mix creates a false dichotomy. Either something is factual or it isn't, if it is specific enough in nature to be either true or false. Some things can be conditionally true, but when they are true, then at that moment and under those conditions, it represents a fact. So in the list above, including the religious statements, a devout Muslim would answer the last three as fact. But he would decide that the first three religious statements were opinion, and wrong opinion at that. On the other hand, a devout Christian would answer fact to the statements about God and Jesus but would say the Allah and Mohammad statements were opinion. Taking only the six statements related to belief, it is not possible for all of them to be fact, since some of them negates some of the others. For example, Allah cannot be the one true god if God exists as Father, Son, and Holy spirit. And every word of the Koran and the bible cannot be right since some passages in each book contradict what is said in the other. Since there is disagreement over the factual nature of the six religious statements, then the logical conclusion is that they represent opinion. If any of them represent fact, nobody knows for sure which ones do so. So it is each person's opinion as to which ones are factual.
And that is how belief differs from fact and from opinion. If something is an opinion, even the person who holds that opinion will usually admit that it is just that, an opinion. But those who hold a particular religious belief will make no such admission in most cases. To devout Christians it is a cold, hard fact that Jesus is the Son of God who died on the cross. To devout Muslims, Mohammad was the greatest prophet of all. To observant Jews there were no prophets beyond their Torah. And all three groups consider their belief as factual. Most ardent followers of one religion or another not only believe that their holy book is absolutely true, but that all the other holy books are patently false. Thus there is no contradiction of fact. If you don't believe the Koran is true then you don't have to take it into consideration when you claim that what the bible says is factual.
But truth has a quality to it that is often inconvenient for the believers. The truth stands as an independent entity. The truth is not affected by opinion or belief. Truth is truth independent of your belief to the contrary. Truth is also not dependent upon knowledge. Facts remain true whether anyone knows about them or not. When you strongly believe something is true but there is no way of knowing it for sure, or even in the midst of evidence to the contrary, it is called faith. In Christian circles, faith is a good quality to have. The bible strongly supports faith. But if you drill down into the nature of faith, you find it to be hollow and ugly. Does God exist? Was Jesus resurrected? Unless you know for sure, based on solid empirical evidence, then you don't really know the truth; all you have is faith. And, by definition, what you have is a strong belief in something for which you do not know the facts. You are taking an opinion and making the claim that it is a fact without any evidence to back it up. That is pretty much the definition of delusional. It is dishonest, and if you teach it to your kids, you are being dishonest with them.
Children learn to cope best when they can recognize the difference between fact and opinion. Some opinions are easy to recognize as such. But religious beliefs are mere opinions masquerading as facts. And when different versions of the facts collide, trouble often ensues.
In closing, let me include a list of cold, hard facts that my students learn are true sometime during the course:
Everything is made of atoms.
We really did land on the moon.
The earth is spherical and goes around the sun.
All life on earth really did evolve from a common ancestor.
The earth is 4.5 billion years old.
The universe is 13.7 billion years old.
Our universe began with a big bang.
And before someone jumps in with the claim that some of these are not really facts but theories, let me remind them that a scientific theory is something that is accepted as true and useful to virtually all scientists and can, for all practical purposes, be reported as factual even if small details of the theory still need to be filled in or improved. For example, the earth is 4.5 billion years old. But that figure was fine tuned downward from a previous estimate of 4.6 billion years. But that does not mean it might actually be only 6,000 years old though.
By the end of the course, if nothing else, my students learn how to recognize an opinion and how to distinguish opinions from facts, even opinions that pretend to be facts.