Religion, say, the Christian religion, fixes definite doctrinal qualifications on its adherents. A Christian, in order to be a Christian, must assent to historical articles of faith, which is to say s/he must agree to 'believe' formulations concerning divine realities that s/he may not 'know' to be true or false. For example, a Christian has no other recourse but to believe in the incarnation of Christ. That same Christian, however, also has very little, if any, recourse to actual knowledge of the Christ s/he states belief in.
This leads to a confusion in terminology wherein the distinction between belief and knowledge is blurred. Some well-meaning Christians think that because they believe a given proposition -- e.g., there will be a mid-tribulation rapture -- they therefore know that proposition to be true. Conversation, at that point, becomes stunted. How can I discuss things intelligently at that point if the person I am talking to equates belief with knowledge? Crudely put, it is possible to believe that elephant ears act like wings when no-one is looking, or that cats house the souls of dead philosophers, perhaps that Darwin didn't die but underwent a rapid acceleration to a new evolutionary stage. It is not possible to know any of that.
So then, what is belief? Belief is, as the English philosopher Colin McGinn put it in Jonathan Miller's A Brief History of Disbelief:
"...what you'll act on, what you'll take for granted, what you'll assent to, what you might gamble on. That means you're committed to that being the case. 'Belief' is really just an umbrella term that covers all the varieties of assent, of takings to be true."
As such, a person can validly use the term 'belief' to state that s/he believes in eco-awareness, democracy, liberal politics, the existence of God or gods, or what have you. To state a belief then, it would seem, is the formal expression of implicit or informal trust in this-or-that phenomena or noumena on a case-to-case basis.
But to carry the definition of belief forward a little more, both Miller and McGinn acknowledge belief as a disposition. This is an important qualification since it realises the difference between what one knows and what one takes for granted; that is, believes. A Christian simply takes for granted the resurrection of Christ because it is a belief stacked on top of another belief that what the Bible states about Christ is revelation from God himself. However, belief in the resurrection comes with no actual knowledge of its truth or falsity. It is a willing leap based on a pre-disposition (i.e., already assumed belief) that what the Bible says is actually true. Belief is therefore dispositional, continuous and assumed, non-episodic, or second nature.
This is in contrast to knowledge. As Miller puts it:
"Although 'belief' resembles 'knowledge', there's a very important difference between the two. In the case of 'belief', you can say that someone believes X and that he was wrong. But it sounds rather odd to say that someone knows X and is wrong. It's part of the definition of knowing something that it is the case. Whereas believing something is a state of mind about which you could be proved to be wrong."
To 'know' something then, is to suggest that something is incontrovertably what it is, and not something else. To 'know' a thing is to perceive its correspondence to testable, communicable reality. But to 'believe' something is to take on trust what might, at some point, be shown to be false.
This puts Christians in a precarious situation not just amongst unbelievers, but amongst themselves, too. For how can conversation happen when belief is taken to be knowledge? In other words, how can anything intelligible be conveyed about any one of the tenets of Christianity if a Christian is convinced that what s/he believes is what s/he knows? The dissonance this creates in the mind of the observant listener shuts down any chances of mutually beneficial dialogue since this blurring of distinctions results in wrong-headed dogmatism, fanatacism, and extremism.
Even if a religious believer is benignly fanatical -- e.g., Catholic assertions about Mary's perpetual virginity, Baptist promulgations on the dance-leads-to-sex scenario, Pentecostal insistance on the gift of tongues -- the fact of the matter is that believing is not synonymous with knowing. As long as the insistance that "because I believe" is directly proportionate to "therefore I know" continues, most, if not all table-talk about religion will be mostly notional and not actual; connotative and absent of the denotative ingredients necessary to intelligently describing a belief, or sharing some actual knowledge. In essence, confusing 'belief' and 'knowledge' makes conversation almost meaningless.
That would be shameful for a group of people charged to "give a reason for the hope that is in you" (1 Peter 3:15, ESV).