I have been thinking about how much we can know and more importantly: which knowledge should be relevant to us? First I will explain my thoughts to you. They will end in a questionable conclusion for which I need your help to reassess it:

Descartes as well as Matrix (the movie) and the "Brain in a vat" thought experiment show us that we actually know nothing about our physical state. This fact is frequently used to create horror scenarios, which shows me: Ignorance about our physical state is commonly seen as extremely negative.

But how about our immaterial state? As Descartes' "Cogito ergo sum" already pointed out, at least our thoughts truly exist. But this also applies to our feelings, right? As sure as a specific thought exists in a specific moment, just as sure a specific feeling is felt in that moment, too (irrespective of where this feeling or thought originated). I apply this same argumentation on our memories, our fantasies, dreams etc. In other words, we can be 100% sure that everything immaterial about us truly exists.

If everything immaterial exists for sure, why should our ignorance about the material world bother us? If you set aside your prejudices, you can agree with me that everything you experience is valuable only because of its immaterial effects such as happiness. More examples, why the material origin of the immaterial should be unimportant:

  1. The Big Bang theory states that our whole universe originated in nothing. No god, no motivation behind all this, but that doesn't make our universe less valuable.

  2. If a child was born from drunk and criminal parents, the child itself is just as valuable as any other child regardless of its origin.

All this leads me to the conclusion, that we really shouldn't care about our physical state, because the value of our immaterial experiences remains the same in any case. But that would mean that we could as well trade our physical freedom for a peaceful simulated world, and this is where I hesitate. Can that really be correct? I ask you to find some reasonable arguments against this.

  • This seems a little unclear to me -- it might help if you could maybe provide references to the Descartes you are working through? Also keep in mind great questions ask about one specific problem -- feel free to break a complicated concern into several related questions if you wish.
    – Joseph Weissman
    Jan 29, 2012 at 21:41
  • I am not sure, which work I read because in school we just had an abstract from it. But in it he introduced his "cogito ergo sum". I only mention Descartes, because I agree with his argumentation that we know nothing except for that the thought exists and that therefore the thinker must exist. It is not necessary to proof the existence of a thought, because I experience it in the very moment it appears. And with the same argumentation feelings, imaginations etc. exist as well. I don't know how I could break this question into smaller ones :(
    – x squared
    Jan 29, 2012 at 21:55
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    This reminds me on the distinction between intrinsic and extrinsic properties. The question would then translate into "Why are extrinsic properties important, if there is no way to measure them?" My own guess at an answer is that this is related to "time". Properties that are currently extrinsic (=properties that are not measurable at present/past) could have an influence on intrinsic properties in the future. So in your example, trading our physical freedom for a peaceful simulated world could impact our future "immaterial experiences" in undesired ways. Jan 29, 2012 at 22:22
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    Descartes argument is circular and doesn't prove anything. First of all, it's about whether the thinker exists, not whether thoughts do (he begins with the premise that thoughts exist), but more importantly the argument is essentially "I cannot conceive of anything that thinks which does not exist, therefore I must exist." But lack of conceptual ability does not prove anything. I know of numerous people who fail to conceptualize determinism; if everyone was like that, would that mean that determinism as a concept does not exist?
    – stoicfury
    Jan 29, 2012 at 22:35
  • @stoicfury: Yes I understand, that the existence of thoughts is a premise to proof the existence of the thinker. But he does so, because he (like me) finds it uneccessary to proof the existence of thoughts. Do you think it is? Because I really cannot see how thoughts could not exist.
    – x squared
    Jan 30, 2012 at 12:26

5 Answers 5


You seem to be discounting the value of the type of knowledge that we can actually have.

I know, for instance, that hitting keys on my keyboard in the appropriate context results in a message that you can read. I also know not to walk into walls, and that I will starve if I don't eat.

Even if the "true" state of affairs is a sensible concept, it is nonetheless enormously problematic if you walk into walls and starve even if you have no idea whether these things correspond to your actual physical state. So ignoring our physical state is apparently a bad idea (or is a vacuous commandment if everything that happens to us forms part of our "immaterial experiences" also).

In any case, you're revisiting heavily discussed and debated topics in epistemology (albeit with a rather unusual conclusion). Locke and Hume (on Wikipedia first, I suppose) are good places to start when considering the consequences of having uncertain knowledge and yet trying to build a reliable model of the world and perhaps even do philosophy.

(Also, incidentally, I'm not sure it's universally accepted that a child born from drunk and criminal parents is just as valuable as any other child, so this is a questionable premise to adopt--it at least requires some argumentation to support it.)

  • You say it'd be a bad idea to ignore our physical state. I say it'd be a bad idea to ignore our perceived physical state (which in other words is our immaterial state). If in the simulated world food is needed to satisfy hunger, I'd eat. Actually my motivation behind this question is, that I wonder if those horror scenarios about being trapped in a nutrient solution and such are horror scenarios after all. Why should we fear a possibly terrible real physical state if the simulation hides it perfectly? And then, if we really don't care, than we could as well do that trade... could we?
    – x squared
    Jan 30, 2012 at 12:47
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    @fuchsgeist - A genuinely perfect simulation is different from reality how, exactly? The typical source of horror is that the simulation isn't perfect and it's designed in such a way to frustrate some of our most important goals. Buddhism has been (in some guises) completely comfortable with reality being an elaborate near-perfect simulation, and nobody seems to be horrified.
    – Rex Kerr
    Jan 30, 2012 at 15:32
  • Oh, I didn't know that about Buddhism. I think I will read up on that, thanks. But a perfect simulation is different from reality in the sense, that physical events don't really occure. That also includes the physical existence of other people. I thought most people would find it disturbing if for example people they love were nothing more than (a really good) imagination.
    – x squared
    Jan 30, 2012 at 15:55
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    @fuchsgeist - How would you know that you were any more real than they were? (And Buddhism isn't exactly about reality being a near-perfect simulation, but it does place a tremendous emphasis on seeing the true nature of things (wherein basically everything is illusory), which is effectively pretty much the same thing.)
    – Rex Kerr
    Jan 30, 2012 at 15:59
  • After breaking my head with no solution, I guess I can't. But to answer my original question this isn't important. What surprises me is that no one seems to have an argument against this trade thing.
    – x squared
    Feb 2, 2012 at 12:08

Your question assumes that we have an immaterial state. There's no evidence to suggest that this is the case: even if you are a brain in a vat, you might only have material state--the current state of your physical brain as various inputs are produced by some other thing. Your state is only and always material.

There is a logical progression out of the vat, and it goes something like this:

Once you accept that there must be at least two distinctions, the "I" that you commonly think of as "I" and the "it" that is defining the restraints of apparently physical reality, and that the "I" part is distinct in some way from the "it" part, it seems most reasonable to believe that other people, since they appear to be just like me in most other ways, are also parts of "me" that experience themselves as "I". From there to believing that a goldfish has an independent experience of reality isn't that far to go.

So the world appears to behave in a way consistent with the hypothesis that there is a physical reality, and reason informs me that even if this is not the case, the part of reality that I commonly conceive of as "I" is constrained to behave as if it occupies a physical reality along with other bits of reality that appear similarly constructed and constrained. By seeking to understand these apparently physical restraints we may either improve our experience of and within the system of constraints or discover the nature of the system of constraints. Furthermore, one of the constraints appears to be that if there is no physical system involved, learning is impossible... so the only thing we can learn about is the apparently physical universe.

  • I like Putnam's way out better, because simpler: Just by imagining you could be a brain-in-a-vat, you cannot be a brain in a vat; because the referents ("brain", "vat", etc.) cannot possibly match between the two conceptual levels. (Thinking they can is an equivocation fallacy.)
    – Jeff Y
    Feb 26, 2016 at 23:43

Since we were born until now, we are living in this material world, mostly. It makes us very intense to the world (physical state). And when someone said that where we live is nothing, naturally it will make us aware there will be great loss on our life.

It will make people realize there is something wrong in our life. But actually, there is nothing to be worry about. Because as already asserted in this question, that we still exist. We still have consciousness. We can dream. Everything is okay. Why should we bother? We shouldn't.

But we must concern on different direction. Those are:

  • We have to understand that if reality on everyday life is just illusion, simulation, nothing or similar to these, then it has the same weight or at least less real compared to dreaming and another immaterial state.

  • Therefore mostly we don't have to put our effort to physical state and we have to start giving our effort to understand another realm (immaterial state) with the same portion to physical state, or at least we have to give appropriate effort to explore immaterial state proportionally compared to as we did on physical state.

The point is:

The moral behind this is, that understanding the facts about physical state must put our effort on two different states (physical state and immaterial state) to balance our life, to balance our possibilities, to make us better human, to make us aware that there is another state that can be considered as real as it can help us to improve our life. To make us realize that we have choices as big (or even bigger) as we ever did on physical state.


This is an oldie but I'll give it a go. 1- Descartes seems to have made a mistake: something thinks, that may not be the "I" that we are used to. 2- You made a mistake: the conclusion according to Descarte (if his reasoning were to be considered correct) is "I exist", not that subjective experiences themselves are real. So neither can you conclude that your experiences are real in the way you perceive them to be real, nor subjective (as that may be - and likely is - an illusion, being there simply material actions such as maybe brain chemistry and electronic action).

  • Interesting thought on a certain level, but Descartes makes the ssame point re 1. Also pretty much wrong about Descartes' argument in Meditation 2 on your point 2.
    – virmaior
    Dec 28, 2015 at 4:11
  • But descartes never actually solved it (he never demonstrated that his "I" is the "I" we are used to). As for point 2, I was wrong. What has not been demonstrated is that external states are any different from internal states.
    – TCN
    Dec 28, 2015 at 18:14
  • But why do you think Descartes sought to prove the "I" is the "I" we are used to. He never claims that's what he's trying to do.
    – virmaior
    Dec 28, 2015 at 22:22
  • Because descartes did not show that it is "I" who does the thinking. As you pointed out: he conceded to that. Meanwhile, the OP appears to have been mislead on that very point.
    – TCN
    Dec 29, 2015 at 2:21

You claim that we can't know anything about our physical state. You use the brain in a vat idea as your rationale for that position. But you are tacitly assuming that knowledge is justified true belief, which is wrong for reasons explained here: Is everything just an opinion?. Short version: knowledge is conjecture controlled by criticism. What matters is finding ways to correct your mistakes, not trying to show you're right, since the latter is impossible but not the former.

Now you claim that I can't know whether I am a brain in a vat. First note that it is still the case that you have many complex experiences even if you are a brain in a vat. The standard explanation is that those events are really happening, and all you have done is take some or all of those events and attached a label that says "not real". So you have taken the standard view of reality and added an unexplained complication. Since the complication is unexplained, that is is a criticism of the complication and so it should be eliminated. See "The Fabric of Reality" by David Deutsch, Chapter 4 for more about this.

Now, you say that we should be willing to trade our experiences for those in a peaceful simulated world. There is a problem with this option. You can only simulate something if you understand it well enough to write a program to simulate it. So your proposal requires limiting people to doing a load of stuff that is already understood. It prevents people from dealing with lots of stuff we don't understand and limits progress.

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