Accepting that belief and knowledge are two very different things, what do we mean by belief and when, if ever, is it useful?
Belief is something that happens inside our minds regardless of what is happening in the outside world. It is a function of the emic world, not the etic one. Something you believe may or may not be factually true, but you do not objectively know for a fact that it is true.
No matter how adamant a person is their beliefs are correct, no amount of conviction can substitute for knowledge. This does not mean that knowledge is inherently superior to belief, just that the two words are not interchangeable. There is nothing wrong with belief, but it is important to recognize what is belief and what is knowledge.
For example, my interpretation of the Fall of Adam and Eve is my belief. I cannot objectively demonstrate it to be true so I wouldn’t want to call it knowledge. I am quite convinced it is the best and most useful interpretation to the point where I no longer seriously consider any of the other interpretations I’ve come across. I also believe that it is possible that one day we may have conclusive proof, and therefore be able to say we know, this interpretation is correct.
Sometimes it is better to believe something than to know it. I can think of a number of cases where I would want to believe something but not explicitly know it.
One simple example is being in a relationship. I would much rather believe my partner is being faithful. How would one objectively and conclusively demonstrate their partner is not cheating on them in order to know they are being faithful?
One way would be to know your partner doesn’t have any opportunity to cheat by locking them away in a dungeon or otherwise preventing contact with other people. Another way would be to have knowledge of the activities of your partner 24/7 by hiring a private investigator to follow them around or constant video surveillance. While these tactics would surely be effective and conclusive, I wouldn’t want to be in this kind of relationship. I can’t imagine how any method of getting conclusive proof would be healthy.
Instead, I’d much rather be in a relationship where I believed my partner was being faithful. Being in an open, honest and sexually-satisfying relationship may be a good enough reason to believe.
Of course, I’m not suggesting to always completely ignore the possibility of infidelity in a relationship. If you have reason to believe your partner is cheating, it might be irresponsible of you to not try to find out for sure. Trying to prove someone is cheating is very different from trying to prove someone is not. Lack of evidence of something is not evidence of the lack of something, but it is probably a very good reason not to believe.
Reasons to believe something can be anything because belief is subjective. These reasons will also be subjective. If a person believes something they will have a reason to believe it. Whether the reasons are sound or not doesn’t change that the belief is still being held.
Beliefs can get dangerous when we try to force them on other people, forgetting that our beliefs are subjective, confusing belief for knowledge. It is also irresponsible to hold beliefs contrary to knowledge available to us. Even worse is to act on those subjective beliefs to the detriment of others. There are, and have been, politicians in America who have believed environmental policy was unnecessary because good Christians would be raptured long before it became an issue. One allegedly went further to suggest worrying about the environment was sacrilege because it doubted that God would take care of us. If people merely believed these things, that might be fine. That people are basing environmental policy — which we all have to live with — on them is another thing entirely.