> If Chase is right and we can't know anything for sure, why do we nonetheless continue to act as though we can?

Well, cognitive science research shows that the brain constantly makes probabilistic inferences about the world, discarding old inferences and making new ones as it receives new sensory input (evidence). So philosophy aside, this science suggests that the brain is an optimizer, always trying to find and act on the most likely hypothesises (sp?) given the sensory input. Perhaps the hardest part is figuring out how the brain interprets the input. If you glance in a room, you don't memorize everything in it, but you might remember certain salient details, like who is in the room and what they are doing. A person is sensitized to notice certain things by his preexisting theories, conscious and unconscious. How our brains decide which parts of our sensory input to consciously notice is, I'm pretty sure (an ironic interjection), close to the heart of the epistemological dilemma and those two essential questions. Whenever our brains choose to notice one thing over another, then the noticed thing is implicitly defined as more meaningful than the unnoticed. How much faith we put in this fallible process of filtering out "meaningless" input perhaps determines or is determined by our certainty in "what we know."

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Adding a bit to Genya's comment, I'd like to say that despite our best efforts, often we miss the most apparent things. I read an article on the Scientific American website that descibes this phenomenon, known as inattentional blindness (read it here; the videos used can be found here). As for my response to the question, we must act as though we can know something for sure in order to maintain our higher-level functions. For example, if you can't be sure that we have all read the same Hamlet text, how can we even begin discussion and analysis of it in class? In order to proceed, you must assume that at least a majority has read the same text. Or, how can you be sure that we have actually replied to this question and have not instead found someone else to answer it for us? Sure, the honor code is supposed to prevent us from doing so, but can you be sure we adhere to the honor code? You can't grade these responses without first assuming that you know that the person who has signed it is the person who wrote it. Our society is built upon previously gained knowledge. If we lose our certainty in that knowlege, our society would collapse.

I agree with Hubert and Genya that, essentially, we act as though we can know things for sure becuase, otherwise, we wouldn't be able to function. Most people who seriously consider the question of knowledge will realize that we can't really know anything for sure, but experience shows us that when we act on what we think we know, 99% of the time, we get the expected (in a general sense) outcome. I would say that even our lower-level functions must be maintained by acting like we know something. Most people usually act based on previous experience, even if they do realize deep down that they might be wrong. For instance, if I moved and went shopping at a new grocery store that looked pretty unsanitary, I would recognize that the food there might be terribly poisoned, but would nonetheless try eating it once. Otherwise, I would die, so I put what I think I know aside and eat. So what if the next morning I wake up very sick? I won't ever go to that grocery store again, even though, being a skeptic, I recognize that I could have just happened to get sick overnight, or it could have just been that one fruit that was bad. Honestly, in my (almost) 17 years of experience acting on what I think I know, life has turned out pretty well, so, by default, why should I change? On second thought, it may also have to do with how willing one is of taking certain risks, the biggest one of which that comes to mind being that of religion - the only one in which I (and most people) don't have direct experience to base my decision upon (unless you count the Unitarian "trying different religions"). If what I think I know as absolute truth is wrong, then there are some huge consequences. But based on my experience and study, that's a chance I'm willing to take.

If Chase is right and we can't know anything for sure, why do we nonetheless continue to act as though we can?

I agree with the idea about how we continue to act as though we know some things in order to function. However, I believe that it is more than just functioning in life as humans, but it is also a central part of developing ourselves as people and society as a whole. By acknowledging that Chase is right even though I cannot know for sure if he's right, I am setting up within myself a system of right and wrong that I would believe in. I now have a base for comparison to compare other new ideas to when I encounter them and then can “label” them as right or wrong. However, the first comparison of ideas comes from comparing Chase’s idea to what limited amount knowledge that I might have prior to hearing it. In other words, comparing his idea to my previous experiences, which have become parts of my “knowledge.” Thus, I, as a person, develop intellectually as more ideas become a part of my system of right and wrong. However, as more people agree on the acceptance of more important ideas, our society is able to move forward and develop into a more advanced society. For example, through the acceptance that the use of machines is right because it helps people with tasks that are dangerous and can be done faster by them then our society keeps on using machines to improve our world. Therefore, the general concept that I’m proposing is that by acknowledging that someone is right helps create a system of right and wrong within yourself that helps improve you as a person. As more people acknowledge someone’s idea then society is also able to improve as a whole.

I think that as humans, we need to make certain assumptions in order to move on in life and accomplish other things. In using the example of religion, believers of Christianity are completely sure that God exists, despite the lack of “hard proof” showing that He does exist, so that they can place themselves in the “grand scheme of things” and move on to more concrete dilemmas – such as finding food. (I merely use Christianity as an example; other religions and atheism apply as well.) Also, I particularly liked Alice’s explanation: that when acting based on experience, we get an outcome as we expect for a large enough fraction of the time that we can say that we “know” something.
On a tangent: Personally, my urge to act as though I am certain of something (that I cannot possibly be certain of) increases if someone else is trying to convince me that it isn’t true. Although this may just be a bad case of adolescent rebellion, it is still another type of situation where I act as if I’m completely sure about certain things, and I think that many other people (not adolescents) also have this streak of defiance. So this could be the reason sometimes...

Given that Chase is right, and that we can't know anything for certain, we continue acting as though we know something for simplicity's sake. Were the world to accept that everything you thought you knew was uncertain, chaos would ensue. In keeping the assumption that you can know something, people don't question everything, they accept an answer when it comes from authority and leave it at that. Were nothing certain, nobody could be correct and nothing would ever get done, but by assuming that you can know something, and that other people can know something, you no longer question every bit of information. People assume and act as if they know something as a way of keeping order in their lives.

If as Chase's Matrix example suggests: we can never be sure of anything why do we continue to live our lives acting as though we can?
As some have already suggested above it is out of necessity.
While ultimately we all have the option of whether to live or not, most people would agree that this is more of a technicality and in practice it most certainly is (the vast majority of people do not end their lives because something is troubling them). And so if we are to accept that we all choose to live then we must next consider how we wish to live. We could question everything knowing that we will never have the correct answer but as Joe suggested "chaos would ensue and nothing would ever get done". Instead we choose to act as though we can know something. We assume that if our knowledge comes from some sort of authority or from experience then there is a great likelyhood that in fact that which we assume is true. And since as Alice pointed out, when we do assume something because it is something authority or experience has taught us, things tend to happen as we expect and our world rarely comes crashing down. So we continue on with lives acting as though we can truly be sure of things because it works and because we must.

Again, as other's have said we continue to act as though we know something because we simply have to. If we constantly questioned the validity of everything, we would never get anywhere. Who would want to live in a world where no one trusted anyone, or anything they said or did? I am generally a very trusting person, I'd like to think that when people tell me something, that it's true. However, I think experience is a very important part of this. Even if we can't be certain of anything I think we choose to go by experience. I tend to trust first, then if through experience the person turns out to be untrustworthy, then I will know to be more skeptical in the future. But, if I embraced the idea that i couldn't be sure of anything, and never trusted anyone, how would relationships be built? Just as we like to hope that we can trust a person and take the chance that we may be wrong and possibly even get hurt, we decide to act as though we know something mostly in order to maintain some form of happiness. Would you rather live your life, well, basically sitting around alone because you've decided that you can't be sure of anything, but at least knowing that you've acknowledged the truth, or would you like to maintain some relative happiness by acting as though you can know something, even though in the back of your mind you're mind you know your life is grounded on something false? I think most of us have chosen the latter.

I'd also have to agree with the other statements here. People require that knowledge be sure or at least fairly certain. However, some of the posts mentioned choice in accepting whether knowledge could be certain. I think that in most situations in their life, people subconsciously accept their knowledge to be absolutely correct and have little choice in questioning it. Sure, in moments of relative relaxation people are at their leisure to question knowledge and subjects of the like, but with the addition of an amount of stress, people often assume their knowledge to be true in order to efficiently move on in their life.

I agree with some of the ideas here. I think there is an element of pragmatism when the brain uses incomplete information to make decisions. There are situations where the brain acts as an optimizer, using fragmentary information be find a best-fit action. But, I think this description only applies to situations where we actually believe that we have incomplete information. Really, I think that we act as though we know things for sure because, subconsciously, we actually think that we do. In other words, even if we are able to come to grips with our lack of true knowledge in the conversational sense, that realization does not change the underlying mechanism which controls how we think. The statement "I can't know anything for sure," just becomes a new absolute which is added to the other things that we "know." So, for the purposes of action, everything we know becomes sure.

My entry is mostly dedicated to a critique of the question itself rather than directly answering it. My reason for avoiding a direct entry all comes down to ontology. The question presupposes a "we" that is capable of uncovering that nature of knowledge, rejecting knowledge, and acting as though it has knowledge. If "we" are to reject that there is any absolute objective knowledge then the "we" that goes along with that subject-predicate proposition must also be discarded.
However, in practice, such "purity" is rarely used. In fact, a reality--or a perception of reality--is always constructed and this construct includes ourselves. The very recognition of ourselves as knowable entities--using the word "we" itself--contains the assumption of knowledge.
The question that we are asked, why do we act as though we have knowledge if we don't, is an absurd question. This is because the statement "we don't have knowledge" contains the assumption of "we"--which is a knowable entity. Therefore, that which we are questioning contradicts itself. If the criterion of non-contradiction serves as an adequate standard by which to judge logical propositions or systems then "we" have every right to question the statement "we don't have knowledge". To say we "act" as though "we" "do [have knowledge]" also contains, in of itself, three other statements about what "we know". The conception of an acting entity that can rationalize its actions is a proposition about a thing in itself--perhaps the most fundamental one, the "self" we identify as "I". Thus, in the statement itself, indeed in this analysis of the statement, we see that there are plenty of relations between objects in themselves and known predicates to associate with them.
I think that the analysis of the question yields an answer to itself. If we are indeed able to make all of these pressuppositions ("we" being used in the most ironic sense possible) then we have already rationalized why we make them. To actually rationalize such a priori knowledge that comes before any ability to communicate (which assumes an epistemology and an ontology) is to say that the rationalization (a distant object that precedes such written analysis) is an object in-of-itself because otherwise we couldn't know it (in the corresponding sense of self with rationalization)--it must exist indepently of the percieved present. Therefore, we would have to rationalize that statement, which requires further rationalization, on into infinity.
Therefore, I think because I am.

An interesting point about Genya's response is that it essentially is a form of logical positivism. The question asked, "If Chase is right and we can't know anything for sure, why do we nonetheless continue to act as though we can?" is answered with a supposed 'scientific' answer--an appeal to cognitive science. However, the question still remains--how can you know that for sure? The reason why I say that Genya's response is in correspondence to logical positivism is that Genya is attempting to put philosophical questions into entirely scientific terms that are supposedly "objective" enough for all of us to accept and which are subject to the criterion of verifiability.
Yet, this viewpoint, as I mentioned earlier, disregards the knower of the information--who must view all of the words that Genya wrote as relating to a system of ideas that then render the reader capable of reconstructing an interpretation of what Genya wrote.
At this point, though, I have run into irony twice. Firstly, I am writing this as if there was objectivity to my viewpoint and referring to a piece of writing that I saw as being available to anyone who might read this--which, according to my piece, is meaningless. Secondly, this piece and Genya's piece both defend the position that people have bias and that any theory of knowledge must recognize this--yet, the initial premise of my piece is denying Genya's "scientific" rigor. What this means is, my piece contradicts itself, while it also both critiques and defends Genya's position (with the same argument).
Furthermore, I would like to state that the apparent contradictions that is brought into a system of knowledge when we communicate (writing a comment, speak a sentence, etc.) lends further credence to the proposition held by many in the class that people pragmatically don't consider all the implications of their actions, cogitations, observations, rationalizations, or what have you.
I think the essential point that we can uncover from this discussion is that people actually don't answer all the philosophical questions necessary to analyze and comprehend everything related to anything they do. Questions such as: "How do we know this?", "Why do we act as such?","Where does meaning reside?", etc. are also "uncovered" (or maybe "artificially constructed" concepts !) when, in the course of human events, it becomes necessary for one people to dissolve the philosophical bands which have connected them with another, and to question, among the ideas of the earth, the assumptions that lead to all sorts of inconsistencies, absurdities and other points of both joy and sorrow.
In the present case, all of us, I'm 100% certain, have come across times where we believed something to be true, only to find out that, in fact, we were wrong. These sorts of cases cause us to look at all of our convictions and try to find a system either by which we can describe the concepts that relate to this all-too-common phenomena.
Interestingly enough, I believe this commentary opens up a new question, "What does communication mean if neither party can be sure they know anything?" "Does communication itself presuppose knowledge?"
The original question that we were answering is simply absurd because on some level it is already answered because we are writing a response. In order to write the response we must have already made the pragmatic assumption of having some degree of knowledge because we put what we thought we know into words. Therefore, any attempt at responding to the question of why we make that assumption is a mere speculation on the assumption that is currently being enacted and must be enacted in order to answer the question. The tangling of the assumption with our analysis of the assumption simply means that laguage itself is tied into that assumption, as is any analysis. This assumption is a nexus that relates to all propositions and renders them all within a single system.
Perhaps if there is any certainty of existence then we can be certain of the assumption that we know something.

Please pardon the following pedantry (or if the concept offends you disregard it all together). I am not attempting to critique an interpretation of Hamlet, I am only trying to remove a misconception about Jesus. In Dr. Raulston's essay, "Clash of Cultures" Achilles is said to be the antithesis of Christ and cite the one set of biblical quotations as your reasoning. However, Christ is not simply a glorification of the weak, the biblical figure clearly, on some level, shares impassioned expressions of power with Achilles. I would like to point out that there are many other bible verses which support this viewpoint.

Jesus Curses a fig tree (out of frustration?):
"On the following day, when they came from Bethany, he [Jesus] was hungry. Seeing in the distance a fig tree in leaf, he went to see whether perhaps he would find anything on it. When he came to it, he found nothing but leaves, for it was not the season for figs. He said to it, "May no one ever eat fruit from you again." And his disciples heard it."
Mark 11:12-14 NSRV
(same story in Matthew)
"In the morning, when he [Jesus] returned to the city, he was hungry. And seeing a fig tree by the side of the road, he went to it and found nothing at all on it but leaves. Then he said to it,, "May no fruit ever come to you again!" And the fig tree withered at once."
Matthew 21:18-19 NSRV

This is a story where Jesus seemingly curses a fig tree just because figs were out of season and he was hungry (I am not excluding any context, by the way, you can check where the verses come from and see for yourself).

Not Peace but a Sword
"'Do not think that I have come to bring peace to the earth; I have not come to bring peace, but a sword. For I have come to set a man against his father, and a daughter against her mother, and a daughter-in-law against her mother-in-law; and one's foes will be members of one's own households (Hamlet?)"
Matthew 10:34-36 NSRV

So Jesus tells people to turn on others.

Jesus Cleanses the Temple
"The Passover of the Jews was near and Jesus went up to Jerusalem. In the temple he found people selling cattle, sheep, and doves, and the money changers seated at their tables. Making a whip of cords, he drove all of them out of the temple, both the sheep and the cattle. He also poured out the coins of the money changers and overturned their tables."
John 2:13-15 NSRV

This is a story of Jesus physically using a whip to drive people out of a market--certainly appealing to his own physical power and strength.

Though, the argument can be made (and, indeed, has been made!) that Jesus teaches that we ought to be pacifistic--his actions reveal a character that was also given to physical violence and conflict. Thus, there are striking similarities between Christ and Achilles.