The blind man and the cave

by Neil Rickert

A blind man is dwelling in a cave.  He is not confined to the cave.  He can come and go as he pleases.  He lives in the cave because he has found it to be a rather congenial place, a place of shelter from the extremes of weather.  Yet he is by no means a hermit or a loner.  He enjoys his frequent walks to the nearby town where he can socialize with others.  He is an avid radio listener, and he uses the radio to keep himself well up to date on the local and national goings on.

Nor is the blind man without modern conveniences.  He has persuaded the electrical utility company to provide him with an electrical connection to his cave.  He frequently uses one of the electrical outlets to recharge his battery operated computer.  His life is significantly helped by the computer, with its talking voice system that can report what he is unable to see on the screen.  These days he uses the computer as his most effective tool for making notes, since he can enter data at the keyboard far faster than would be possible with his Braille writer.

The obsession

The cave itself is quite large.  Perhaps this is one of the reasons that the blind man finds it so congenial.  But, without the use of his eyes, he cannot tell what is the shape of the cave.  He has a rough idea of the ground level of the cave, because he often walks around feeling the surfaces.  But he cannot tell how high it is, nor can he tell what is the shape of that part of the cave which is so high as to be beyond his reach.

Finding the shape of the cave has become something of an obsession with the blind man.  And why not, since it is the place he calls home.

He has, of course, tried the obvious method for determining the shape of his cave.  He has invited some of his sighted friends, and asked them to describe it to him.  But their descriptions have been most unsatisfactory.  In describing the cave, his sighted friends like to point to and talk about a feature that they can see “over there.”  But pointing is of little value to the blind man.  And when he reminds his friends of this, they find themselves lost for words, unable to come up with ways of describing the cave which do not depend on their visual intuition.

The scaffold

In spite of his physical handicap, it happens that the blind man is a skilled craftsman.  He had acquired his skills as a child under the tutelage of his devoted father, himself a skilled artisan. And the blind man has worked to maintain his skills, for it is those skills that have given him a degree of independence that is unusual for one suffering from total blindness.

The blind man is not one to sit around and brood about his fate in life.  Unable to get useful assistance from his sighted friends in satisfying his obsession, he decides to act for himself so that he can discover what is the shape of the cave.  So he heads to the local hardware store, and orders some steel bars (angle iron) that he could use to erect a scaffolding within the cave.  He also orders suitable bolts that he can use in his construction.

On the next day, when the delivery truck arrives with the steel bars and bolts, the blind man sets about erecting his scaffolding.  As he moves a bar into place, he attaches a Braille label to it. Next, he carefully inserts the bolts, and tightens up the nuts so that the bar is rigidly in place.  Then he goes to his computer, and records where in the structure the new bar was bolted.  That is, he records which bar was connected to which.  Since the bars are not all of the same length, he also records the length of the bar measured between the centers of the bolt holes that were used for connecting it into the structure.  It is his intention that, by the time he has finished, his computer will contain a precise description of the scaffolding, a complete set of rules which define the shape and structure of the framework he has erected.

The blind man expects that it will take him several weeks to finish the construction of his scaffolding.  He cannot be sure quite how long it will take, and he cannot be sure how many additional steel bars he will need to order before he can complete the task.  But he is in no hurry.  He can work on the scaffolding while he is listening to the radio.  His project has given him something to do with his spare time.

The reason that the blind man cannot be sure how long the construction will take, and how many steel bars he will require, is that he has no complete design planned out for the structure.  He has a systematic methodology, but not a design.  He could not have a design, for to have one would require knowing the shape of the cave, and that is what he does not know.  His methodology is to build the scaffolding so that it will be rigid and strong enough to support his weight.  Then, during the construction, he can climb onto the structure, and reach out to feel how close it is to the sides of the cave, and to the roof of the cave.  If the distance is so great that he cannot reach the stone surface of the cavern, he knows that he will have to further extend his scaffolding in that direction.  His intention is to eventually erect a scaffold which will be a close fit to the shape of the cave.

By now four weeks have passed since the blind man began his project. The scaffolding is complete.  It is a framework which fills out the cave.  The outer perimeter of the structure is never more than a few inches from the surface of the cave.  And the blind man has the complete specifications of the scaffold recorded in his computer.

The shape of the cave

Because he carefully labeled all of the steel bars in the scaffolding, the blind man has a way of designating locations on that structure.  He can use the symbol M3A7 to denote the vertex where the bar M3 is bolted to the bar A7.  But he can also use M3A7 to denote the point on the wall of the cave nearest to that vertex.  Using the construction parameters he has recorded in his computer, he can quickly calculate the distance between M3A7 and G1H6.  Technically, this is the distance between two vertices of the scaffolding.  But because these vertices are very close to the cave wall, it is also a close approximation to the distance between two points on the cave wall.

As a result of his methodical work, the blind man can now truly say he knows the shape of the cave.  He knows it in far more detail than did any of his sighted friends when they tried to describe the cave. The scaffolding that he had constructed was a framework that he could use to help him find the shape of the cave.  The labels he assigned to parts of the scaffolding have become part of a conceptual framework he can now use to describe the shape of the cave.

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7 Comments to “The blind man and the cave”

  1. Hopefully he doesn’t want to “know” the color of the cave, nor how the shape of the cave would look if he had eyes. He’ll never know those things, even though he may acquire knowledge using his other senses. I like to consider our epistemological limitations/indeterminism as analogous to the Blind man. We can try to find ways around a handicap, but some knowledge can only be acquired if that handicap disappears. In the case of us human beings, an entity analogous to the non-blind friends (say an ultra-violet light microscope), would provide us with a means for describing things that we can’t otherwise see, but we’d still lose data after translating it to a visible color scale (analogous to the friends giving an unsatisfactory description of the cave).

    This shows how we can’t know anything fully, without first separating ourselves from the system. Since we can’t ever fully separate ourselves from the system, our “blind man” handicap is unavoidable.

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    • Hopefully he doesn’t want to “know” the color of the cave, nor how the shape of the cave would look if he had eyes.

      He can ask somebody the color of the cave. Maybe he still can’t know, but that’s the whole point of why I disagree with “knowledge = justified true belief”. The blind man could have justified true beliefs about color just as much as any of us. If the blind man doesn’t know the color just from having the belief, then I don’t actually know anything from merely having the belief.

      As for the shape – I don’t know how the cave would look if I had eyes. And I do have eyes. “How it would look” seem bogus to me. It is not a valid question. If I were looking at the cave, I might be able to describe the cave, and no doubt my looking would have been required for me to give that description. But describing the cave isn’t the same as describing how it looks. We cannot describe our own subjective experience. We can only describe what is objective.

      I wrote that parable to illustrate what is involved in gaining knowledge.

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      • “The blind man could have justified true beliefs about color just as much as any of us.”

        His believe of color would be less justified, because he wouldn’t have ever experienced color and so would have much less context.

        “If the blind man doesn’t know the color just from having the belief, then I don’t actually know anything from merely having the belief.”

        That is not correct in all cases. He can imagine what the color would be like (especially if he wasn’t blind from birth), and this would be much more justified — but still less than someone that can actually see the color. So we are starting to quantify the justification of the beliefs here…
        You can “know” things like the size of the cave, just as the blind man can. These things can be described to you, and if you can get a sense of the size description, you’re good to go. On the other hand, in this case, color is a property that you can’t convey to a blind person because it requires sight to experience. So there is a difference here. One belief is based on a description (the blind man’s belief that is) and your belief of what the color is, is based on a lot more than that (previous experience of color and in this case, you could see the cave’s color for yourself whereas he can’t).

        “I wrote that parable to illustrate what is involved in gaining knowledge.”

        It looks like it involved gaining facts (size information, shape, etc.), which was something that you had a problem with in an earlier post.

        -Peace and Love

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        • It looks like it involved gaining facts (size information, shape, etc.), which was something that you had a problem with in an earlier post.

          You must have misunderstood something from that earlier post.

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          • In the previous post when we were discussing knowledge, I said that gaining knowledge is basically acquiring facts and you disagreed with that. In this case, the man is gaining facts (size, shape of cave, etc.) and presumably gaining knowledge and you said that you wrote that parable to illustrate what is involved in gaining knowledge. See the disconnect here?

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          • No, there’s no disconnect.

            I see knowledge as the ability to have facts and to relate those facts to reality. I don’t see knowledge as the facts themselves. The blind man, in building that scaffolding, was gaining the abilities that I count as knowledge.

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          • “No, there’s no disconnect. I see knowledge as the ability to have facts and to relate those facts to reality. I don’t see knowledge as the facts themselves. The blind man, in building that scaffolding, was gaining the abilities that I count as knowledge.”

            I think there is a disconnect. All the blind man needs to know is WHAT he is measuring (a fact), and then know the measurement (a fact). Then the facts that he gains (height of the cave) will be the newly acquired knowledge because he understands the facts based on previous facts learned. It is true that if I memorized the height of the cave, but I didn’t know what “height” was (as well as the units), nor what a “cave” was, nor what a “measurement” was — then I would have “facts” memorized that would be meaningless to me. In your parable, we assume that the blind man already knows what “height” is, as well as “cave” and “measurement”. Which means if he simply gains the new fact of “the height of the cave”, that fact alone is the only thing he’s gained and with his previous knowledge (more facts) of what “height”, “cave”, and “measurement” are, his measurement will have context and he will have gained knowledge based on the addition of that one fact. The key thing here is to realize that the only added information he’s gained is the actual measurement itself — as this was the question he wanted an answer to. The fact was all he needed to gain to get that knowledge (as he already had the facts needed prior to this measurement to give it context) and the scaffold and measurement tools were only the medium for which to gain that fact. He could have just as easily had someone tell him the height in each particular place of interest and would have gained roughly the same knowledge (the only difference would be the quality of information transmission that the computer produces vs. one of the blind man’s friends — but we can assume they are equal).

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