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Vat-Knowledge Is Knowledge Enough

Ilmari Hirvonen

Among the mighty tasks that analytic epistemologists have taken upon themselves is to give an answer to the philosophical sceptic. Simplifying a little, one could summarise scepticism as the denial of knowledge. In other words, the sceptic claims that we don’t know anything or, alternatively, some specific thing – like whether the past exists or whether there are objectively true moral values.

Although there have been ancient and modern thinkers who have called themselves sceptics, in reality the philosophical sceptic is all but a mythical creature that can at best be found on the pages of epistemological articles and books. In practice, the sceptic is more like a fictive sparring partner that the epistemologists have conjured up in order for there to be an adversary to fight against, a challenger to whom one can demonstrate that we truly possess knowledge.

One of the main weapons that the (imaginary) sceptic has in her arsenal is appealing to sceptical hypotheses. A sceptical hypothesis is a hypothetical scenario which is incompatible with some piece of knowledge that we ascribe to ourselves. Moreover, we are unable to distinguish in practise the sceptical scenario and the scenario where our knowledge is actually correct.

Perhaps the most well-known modern sceptical hypothesis is the brain in a vat scenario. In this theoretical situation an evil scientist has removed your brain and put it in a vat containing some life-sustaining liquid. In addition, the scientist has connected your nerves to a supercomputer which creates for you the illusion that everything is perfectly normal.

According to the argument, since your brain would in this scenario receive physically identical impulses as it would if it still were in your body, you cannot tell from your perspective that you’re not a brain in a vat. Therefore, you don’t know a number of mundane things, such as whether you actually have internal organs or not. The argument can be formulated as follows:

(1) You don’t know that you’re not a brain in a vat.
(2) If you don’t know that you’re not a brain in a vat, then you don’t know that you have internal organs.
(C) You don’t know that you have internal organs.

Now, even though the conclusion of the sceptical argument seems ridiculous, the logic behind it is flawless. If the premises of the argument are true, then so is the conclusion. Thus, assuming that you want to avoid scepticism, you need to show that there is something wrong with the premises.

And here problems arise. For it is painstakingly difficult – if not impossible – to give good reasons against something that you cannot, by definition, access in any way. From your current point of view or, as a matter of fact, from our current point of view, we cannot really say for sure that we’re not merely bodiless brains trapped in a computer simulation.

Of course, there’s something you could say against the possibility of being nothing more than a brain in a vat. Daniel Dennett, for instance, has pointed out that we aren’t able to produce so credible a virtual reality with our current or future science. Likewise, Evan Thompson and Diego Cosmelli have argued that consciousness requires a body and, thus, we cannot be merely bodiless brains.

These are good points, but they share a common weakness: they assume that the real world, which we cannot access, is similar to the world that we can access. However, the sceptic can modify her account so that we have been trapped in the simulation already from birth. If this were the case, then we wouldn’t know what technology – and perhaps even the laws of nature – would be like in the real world. And, therefore, we couldn’t make reliable inferences about the actual world on the basis of our virtual world.

Despite all this, there seems to be something fundamentally off with the sceptical argument. Think about it. If the argument were sound, then I wouldn’t know whether my refrigerator contains orange juice. But I appear to have really good reasons for claiming that I do know this. I just checked (and it doesn’t). Furthermore, it seems to me that I know this even if the sceptical hypothesis were true.

When I open my refrigerator door, look inside there, and utter the sentence: “I don’t have juice,” I’m making a true statement. My utterance is a correct description of some state of affairs, albeit it might be an incorrect statement of how the metaphysically underlying world is. But, at the very least, my sentence gives a right report of the epistemically accessible world.

Hence, even a mere brain in a vat can still know what kind of a simulation has been fed to it. It is able to have knowledge about the structure and invariances of the simulation. And if this is true, then being a brain in a vat and having internal organs aren’t necessarily incompatible alternatives. You can be a brain in a vat in some metaphysically fundamental sense and nevertheless have internal organs in the epistemically accessible reality. Based on this, the sceptical argument needs to be reformulated as follows:

(1) You don’t know that you’re not a brain in a vat in some metaphysically underlying world.
(2) If you don’t know that you’re not a brain in a vat in some metaphysically underlying world, then you don’t know that you have internal organs in the epistemically accessible world.
(C) You don’t know that you have internal organs in the epistemically accessible world.

It is easy to see that the second premise in the argument is false. The fact that you happen to lack this kind of metaphysical knowledge doesn’t deprive you of all sorts of knowledge. You can know what the epistemically accessible world is like and, amongst other things, that you have internal organs in it. In a word, brains in a vat can possess vat-knowledge. This is the kind of knowledge that you can have irrespectively of whether you are a brain in a vat or not. And besides having vat-knowledge, they can also do vat-science in order to examine what the accessible reality is like.

To be quite honest, I must admit that I haven’t really given an answer to the sceptical hypothesis. For I don’t claim to have shown it to be false. Now, I dislike scepticism just as much as the next person, but I also think we should give the devil his due. Scepticism does indeed show that some types of knowledge are out of our reach. But it only demonstrates that we cannot possess a certain kind of metaphysical knowledge. Knowledge concerning the accessible reality, the only reality that is of practical importance, is still up for grabs.

Understand that I’m not trying to solve scepticism here but rather to dissolve it. This is a plea for not taking it seriously. My claim is that the metaphysical knowledge which is destroyed by scepticism wasn’t that important to begin with. Note – and this is very, very important – that if the brain-in-a-vat scenario is true, then all of our current knowledge actually is vat-knowledge. And we haven’t been doing so bad thus far, have we now? In fact, I personally am quite satisfied with vat-knowledge. What more do you really need to know?


Dennett, Daniel C. (1991): Consciousness Explained, New York: Little, Brown and Company.

DeRose, Keith (1999): “Introduction: Responding to Skepticism” in Keith DeRose and Ted A. Warfield (eds.) Skepticism: A Contemporary Reader, Oxford: Oxford University Press, pp. 1–24.

Pritchard, Duncan: “Contemporary Skepticism” The Internet Encyclopedia of Philosophy, URL =

Putnam, Hilary (1998): “Brains in a Vat” in Reason, Truth and History, 1981, Cambridge: Cambridge University Press.

Thompson, Evan & Cosmelli, Diego (2011): “Brain in a Vat or Body in a World? Brainbound versus Enactive Views of Experience” Philosophical Topics, vol. 39, no. 1, pp. 163–180.

Published by Ilmari Hirvonen

PhD student at University of Helsinki working on philosophy of pseudoscience. Dabbling in some philosophy of religion in spare time.

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