"I do not know, but I believe." This is a common saying amongst many people at some time or another. Perhaps, when we say this we seek to be intellectually humble. Perhaps we wish to remain open to differing opinions lest we blind ourselves to the truth in dogmatism. But saying this accomplishes neither of these things, chiefly because this statement is always false.
If you do not know something, then you could be wrong about it. You only know something if you are certain about it. Thus, if I say, "I do not know this, but I believe this." That entails, "I believe this, but I may be wrong about this." That is the same as saying, "I believe that this could be, but it could also not be."
Something strange has just happened. We began with a statement "I believe" that was purely affirmative. We ended with a statement, "I believe that this could be," which is entirely agnostic. Since either affirmation or negation is a possibility, neither option can claim a monopoly on our belief. Thus, if "I believe this" is the same as "I believe it could be either way," then "I believe this" is the same as "I believe not this."
Suppose someone says that we can only claim to believe something if we believe it more than we believe not it. The problem with this idea is evident in the way it has been framed. If I believe two opposite ideas, one more and the other less, I still believe there is a possibility of both. But if every statement of belief I make is a statement of belief in possibility, than belief expresses mere supposition. However, most people do not understand belief this way. If I believe in God that does not mean I am an agnostic.
Belief is not probabilistic, nor is there any threshhold of certainty for belief. Something does not become a belief if you are 51% certain about it, but not so if you are only 50% certain. First of all, this is because belief is not a question of quantity. Either someone does believe something or they don't. It isn't proper to say that you have 99% belief. You might as well say, "I believe there is a high likelihood it is so," but to say that you believe it is so without qualification is dishonest. Again, someone who believes in God doesn't believe there's a small likelihood that He doesn't exist. We have other ways of expressing sentiments of probability, but we say someone believes something if we mean that they are certain about it.
So then, if the statement, "I do not know this, but I believe this," is never true, then is there any distinction between knowledge and belief? There is. If I say, "you believe this, but you do not know this," then this statement very well may be true. If, however, I agree with another when they say "you believe this, but you do not know this," by saying "perhaps you are right," then I am admitting I actually no longer believe. Thus, statements about the belief and knowledge of others may truthfully differ, but statements about the belief and knowledge of myself may not differ.
But how can the truth of a statement differ based on who is saying it? That is because the truth value of the statement makes reference to the speaker. When I say "I believe this, but do not know this," there are only two possibilities. Either I believe it truly, in which case I must truthfully also say that I know it, since whatever we believe we believe that we know, or I believe that I do not know this, in which case I cannot believe it, for no one can believe what they do not believe they know.
Now, there is a very long tradition of philosophers making a distinction between knowledge and belief based on whether a belief is properly justified with reason by its speaker. This tradition goes back to Socrates and continues to the current day. According to these philosophers, a belief about something that is in fact true is not knowledge, even if the believer sincerely believes that it is true, unless it can be justified by a good reason.
Thus, taking this idea together with what we already know about the relationship between knowledge and belief, anyone who believes something believes they know it. Thus, anyone who believes something must believe that their belief is justified with a chain of irrefutable reason. But is this really so? The way all men act demonstrates otherwise.
Why do we act the way we do? Certainly, our actions are not random. They have the intention to accomplish some end through action. Now, it is possible that we know that our actions will accomplish their ends, or we do not. If we do not know that our actions will accomplish the ends we intend them to, then we will not act, because we have nothing we seek to accomplish with our action. Now, one may say that they do not know their action will accomplish its end, but they do believe it will. However, if one believes their action will accomplish its end, they also must believe that they know their action will accomplish its end, since no one can separate their own knowledge from their belief, only the knowledge of others from the belief of others.
Now, it is also possible for someone to say that they know an act to be intrinsically good regardless of whether or not they know that it accomplishes any good end. But is it really good to merely pretend to be doing good deeds even if you have no idea what their consequences are at all? For example, if I want to help someone by repainting their room, this would not really be a good act at all if I did not believe that the person whose room I was painting wanted their room to be painted. Most virtuous actions are only virtuous according to the conditions in which they are practiced. If my actions may do nothing or may in fact be harmful, then they are not in fact good deeds at all, they are just actions that make myself feel good at the expense of others. Likewise, if I seek to plan for my future by doing my homework, but I do not actually know that I have any homework due, then I am just wasting my time by doing something worthless. And where does the knowledge that an action is good come from? It is not something that can be proven by logical means, even though we think we know it.
Some skeptics have also claimed to have their actions guided by "nature." This nature is a blind instinct that carries them along through everything they do but is not based on any kind of reason. Presumably then, everything such individuals do and say must be mere instinctual acts that carry no meaning or reason in them, only arbitrary whim, like a wild animal. But then they cannot possibly be capable of saying the truth about anything since they do not know the truth about anything and do not speak with intentionality.
Finally, it is possible that we know nothing, but our actions are guided by God. But this notion turns man into some kind of weird puppet, pulled by his strings to do he knows not what by his puppeteer. Meanwhile he is blind to what he is doing and why he is doing it. However, we do know what we are doing and why we are doing it. We are conscious of the ends towards which we act.
So then it is clear that a person's beliefs are made evident by their actions, and that therefore to be honest we must confess that we know that the ends for which our actions are enacted will be accomplished by our actions, or at least that there is a large enough possibility that they will be. There is, therefore, no division between the practical assumptions that a man makes in carrying on his day to day life and his epistemology. Anyone who attempts to make such a division is deceiving himself. To us, the sun will rise tomorrow and objects will not disappear when we look away. That is, to us, what really must be. If one day the sun were not to rise, then I could say that I did not know the sun would rise, but only believed. Now I must say that I know the sun will rise tomorrow, because I act with no uncertainty about this fact and in my consciousness it is always present. I can't force the sun to disappear or force myself to not believe. It will always be there, just as all the memories of what has happened to me will continue to have really happened to me. I cannot say that my memory could be false until I actually have uncertainty regarding its truthhood. Someone else may properly claim that my memory is false, if they believe as much, but I cannot make such a claim, and I cannot affirm that their claim could possibly be correct until I realize as much myself.
So then, can all the daily assumptions that we make be confirmed with a line of irrefutable logic? No. Logic relies on premises, and premises come from our beliefs. But these beliefs are always necessarily "irrational" because they do not depend on rational arguments, but are taken as a given. Thus, it is also very unlikely that most everything I know is "knowledge" according to the standards of most philosophers. But it is in fact knowledge. I know it is knowledge because if I claimed otherwise I would be lying. So how can something that cannot be proven be knowledge? Simply this, that being able to imagine that something were otherwise does not make that a possibility. I can imagine that when I turn my head behind me, there will be a gaping void. Many philosophers would equate the existence of such a possible imagination with proof that I do not know there is not a large hole behind me. But that is silly, because it is impossible that there is a large hole behind me, simply for the reason that I cannot bring myself to even remotely believe that it is actually possible. I may imagine such, but lo, I shall turn my head and there shall be reality, just as I expected it to be.
So then, if it is correct to say that knowledge is mainly sourced in intuition and belief beyond mere rationality, why is skepticism so tempting? Why is it that when I said there was no hole behind my chair, I was nevertheless tempted to look, just in case. Belief is strange, in that often what we know at one point we lose confidence in, and sometimes we can even convince ourselves into becoming paranoid about something that is obviously absurd, and then what was formerly impossible becomes possible to us.
It is not as though all kinds of thought are equal. The human mind is finite. It is possible to condition one's mind in such a way that we are clouded from recognizing reality by our own skepticism. Humans have a hard time separating imagination from belief, even though the two are indeed separate, but often, and unfortunately, our imagination feeds into our beliefs and causes us to doubt what we once knew.
Imagination should be good, and it is possible to imagine something that we know to be false without being led into believing it. That's what fiction does. It is also possible that imaginitive fiction could help us to realize something that we did not know before. However, fiction can also change and mold what we consider to be possible in a negative way. It's not a coincidence that many contemporary beliefs about the world that are increasingly mainstream have roots in fiction, and not all of these are good. Seperating what is concievable from what is possible is thus essential. Possibile ideas have some kind of vague association with reality that we are conscious of, pure conception lacks this entirely. It is very commonplace for arguments from skepticism to suggest that strange fiction is a possibility, and that we should therefore be skeptical, however, usually these are not actually possibilities but conceivabilities which have been conflated with possibilities.
There is another timeless non-argument for undermining every form of knowledge. I say it is a non-argument because it does not posit anything, it only questions. "How do you know this is true?" "Why must this be so?" "Show me what this thing is that you believe in. What is it?" "What do you mean?" These are a few of the non-arguments that posit nothing and are intended to demonstrate a lack of knowledge on the part of their recipient. Socrates is famous for these kinds of questions. Asking how someone knows something or what their belief really means makes for a great way to learn more about another's belief, but these kinds of questions do not constitute arguments for the simple fact that they do not argue anything. They merely request knowledge. If that knowledge is not granted to the questioner it does not prove that it doesn't exist.
The best demonstration of this fact comes from a great novella called "Flatland," by Edwin Abott. In flat-land, everything is 2-dimensional, and all the inhabitants of flatland believe nothing can exist outside of those two dimensions. One day, a being from the third dimension enters and tells one of the flatlanders that there is a third dimension, but he flatly rejects this. His rejection, mind you, does not come from having himself any reasons why a third dimension could not exist, but simply from not knowing what the third-dimensional being is talking about and being unable to reconcile it with what he considers to be real. After trying in vain to make sense of what the strange being is saying, which just sounds like nonsense, he finally asks, "And what may be the nature of the Figure which I am to shape out by this motion which you are pleased to denote by the word 'upward'? I presume it is describable in the language of Flatland." Of course, the sphere cannot explain this to the flatlander. He has tried every metaphor, every analogy he can think of, but the two-dimensional being simply cannot understand three-dimensional space, even when described to him in mathematical terms. At last, the three-dimensional being has to resort to force, plucking him out of the two-dimensional world to see what he is talking about.
Sadly, in real life we do not have this option, and often time answers like "what are you talking about?" and "what do you mean?" must go unanswered. However, it is a fallacy to suggest that this implies there is no answer. There may very well be an answer to such questions, but language is inadequate to explain it, possibly because the language is misinterpreted, even as the circle in flatland constantly misinterpreted the sphere's references to "up" from the plane as references to "North" on the plane. Similarly it is common for those arguing about fundamental questions regarding things such as consciousness, God, ethics, aesthetics, and metaphysics to constantly talk past one-another. Abstract words and terms are the very last to be learned, because it is most difficult to draw correlations from abstract words to the phenomena they refer to in the world, which can't be pinned down to a particular object, place, or time. It is easy to learn that any time someone uses the word "chair" they are referring to that brown object that you see. It is much harder to figure out what another person is referring to when they use a word like "soul." For this reason we are prone to develop an entire universe of assumptions about what other people mean when they refer to such abstract words, and when we do not share a common understanding of the language around these words misunderstandings, sometimes irreconcilable, are inevitable.
Nevertheless, when I say that the sky is blue, it would not be a real argument to say, "why do you believe that the sky is blue. No one has ever given me a good reason why it should be so I think it probably isn't." You may say, "I don't understand what you are saying and can't believe in something I don't understand," but then don't assume this means that what another is saying is meaningless or just obviously wrong. They may be seeing something you are not, or referring to it in a way you are unaccustomed to. Sometimes, truths are merely self evident and neither can nor should be explained. And I certainly can't infer that just because other people disagree with me that I don't know what I clearly do. If someone tells me 2+2=5 and seems to genuinely believe it, I will not then doubt that 2+2=4, even if the vast majority of people believe it equals 5.
Now, all of this is not to say that I must believe I am right about everything, but the proper way to determine what I do not know and what I may be wrong about is not to doubt what I already know, but to continue to ask questions and investigate possibilities. It may turn out that something I thought I knew I in fact did not know, but the truth comes via affirmation, not negation. If I don't know something, it's because I'm missing knowledge, not because I have falsehood. Since falsehood is just a lack of truth, the only remedy is knowledge of the truth. If something seemed true to me and no longer does, then it is because I learned something new that changed my mind, not because my old beliefs or intuitions were erased from my mind.
The fact that all falsehood is a kind of ignorance does not mean it is impossible to be wrong, but that when we are wrong about something it is rather a kind of confusion, and in the effort to fully believe in what we believe we will often find that the puzzle pieces of what we thought to be a single coherent thought do not really come together, but were fragmented ideas that only seemed right. Nevertheless, we cannot judge this seeming to be false until we encounter some new knowledge that leads to a broader perspective, through which we see the fragmentation and inadequacy of what was previously believed. This is why it is possible for people to believe things that are in fact paradoxical or self-contradicting. If we really try to believe in a paradox and focus on knowing what truth it is expressing, it is only then that we realize exactly how and why it is paradoxical.
Even the belief in something that does not exist when it really does, or vice versa, is a kind of incoherence. We may think it possible, but it is inconsistent with the nature of existence that such a thing exist, even as it is inconsistent with the nature of evenness that five be even. The act of knowing what exists and what doesn't is the contemplation of Existence, trying to understand the relationship of existence to possibilities to determine if they are real or are not. Now it is difficult to understand what this "Existence" is. We don't know what it is except indirectly and partially, otherwise we would know with ease whether any hypothetical possibility exists or not. Nevertheless, I would argue that Existence is God, Who calls Himself "I Am" and "the Truth." Though this is a line of thought that will have to be continued another time. What is important here is that falsehood is not the result of "bad knowledge" or "bad intuitions" or anything like that, but of a lack of knowing, fragmented and incomplete belief. So, I very well may be wrong about a lot of things, if we understand falsehood correctly as a kind of confusion resulting from lack of truth. Indeed, in general, I believe that I am probably wrong about many things. However, I cannot identify which of the things I know is one of those things, otherwise I would not really believe that I know it.
Now, if I have uncertainty about what I believe in general, doesn't that mean that I have uncertainty about each and everything I believe to some degree? Not so, since I know that the sun will rise tomorrow, but I also know that I may be wrong about something. It is not as though the uncertainty in general distributes to each particular thing I believe. While it might be a strange statement to say that I know 100 facts with confidence, but also that one of these facts is probably false with confidence, it is not a contradiction. It is merely counterintuitive. It is the same as when I read two statements and know with confidence that they are both true, and yet they lead to a false conclusion. I may investigate to see whether I should reconsider the truthfulness of one or the other of these two statements, but until I do reconsider them I may completely believe them to be true. The fact is that we do not really think coherently, even when we try to. We often believe things that contradict each other, and it may be that something I have total confidence in is really false, but I do not know that or even consider that this thing could be one of those possibly false things that I believe. Again, the nature of falsehood is fundamentally incoherence and confusion, so it should not be surprising that we are even confused about what we are confused about.
In conclusion, there is a healthy amount of skepticism, but generally speaking there is too much of it. Highly skeptical societies are also societies full of widespread distrust, agnosticism, and depression. Skepticism is sort of like a disease in that it can cloud the mind from knowing what it naturally should know. It blinds us from ever experiencing some of the greatest pleasures in life. Like William James noted, a man who is always skeptical of any woman he meets will never be able to fall in love with her. The same goes for our relationship with God. So while it is good to ask questions about most everything, you should not question everything. Trust is not antithetical to knowledge and questioning is
but a precondition for it.