Are you sure you have hands?

leonardo_aby Massimo Pigliucci

Skepticism is a venerable word with a panoply of meanings. When I refer to myself as “a skeptic,” I mean someone inspired by David Hume’s famous dictum: “In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. A wise man, therefore, proportions his belief to the evidence” [1]. Or, as Carl Sagan famously phrased it, “Extraordinary claims require extraordinary evidence” [2]. Oh, and if there is one thing I resent it is being mislabelled as a “cynic,” meaning a naysayer with no sense of humor…

But skepticism (and cynicism, for that matter!) in philosophy is much, much older than that, and has at the least a couple of additional meanings [3]. According to so-called (by Sextus Empiricus, second or third century CE, [4]) “academic skeptics” (because they belonged to Plato’s academy, post-Plato), such as Carneades (214-129 BCE) [5], we cannot have any epistemically interesting knowledge. A different type of skeptic, the Pyrrhonian (named after Pyrrho, 365–ca 275 BCE) denied even that we can deny the possibility of knowledge, a meta-skepticism, if you will. Few modern philosophers are interested in Pyrrhonism, while academic skepticism has a long and venerable tradition, including perhaps most famously Descartes’ “radical doubt” thought experiment, in which he imagined a Machiavellian demon determined to trick him about what he thought he knew. Descartes then asked whether it would be possible, under those circumstances, to actually know anything at all. His answer, of course, was in the affirmative, and took the form of his famous cogito, ergo sum (I think, therefore I am) [6].

There is, of course, a much more fun way to think about the problem of skepticism in epistemology, and that is by using the 1999 scifi move The Matrix as a philosophical thought experiment [7]. The movie famously begins with our hero, Neo, played by Keanu Reeves, living what he thinks is a perfectly normal life, which soon reveals itself to be anything but. Neo, turns out, is much closer to the famous “brain-in-the-vat” (BIV) scenario of modern philosophy of mind (to be precise, he is a body-in-the-vat), with all his “experiences” actually being fed to him via artificial stimulation for the purposes of an evil post-technological civilization of machines that have enslaved humanity.

There is a crucial scene in the movie [8] where Neo’s mysterious mentor, Morpheus (played by Laurence Fishburne) poses the question to Neo of whether he wants to keep living in the “reality” he knows, or if he has the guts to see “how deep the rabbit hole goes.” As we know, Neo chooses the red pill that characterizes the second choice and the movie unfolds from there.

Neo, of course, is initially (properly) skeptical (in the Humean sense) of what Morpheus is trying to convey. The latter might as well have asked his question along the lines of: “how do you know you are not a brain in a vat?” How would you answer that sort of question? Which is another way of asking: have we made any progress against (academic) skepticism?

My discussion here tracks the one put forth in Steup’s broader treatment of epistemology in the Stanford Encyclopedia of Philosophy [9]. We begin with a quick look at the minimal version of the BIV argument:

(1)  I don’t know that I’m not a BIV.

(2)  If I don’t know that I’m not a BIV, then I don’t know that I have hands.


(3) I don’t know that I have hands.

This is a formally valid argument, i.e. its structure is logically correct, so any viable response needs to challenge one of its premises — that is, question what in logic is called its soundness. Before proceeding, though, we must note (as Steup does) that premise (2) is tightly linked to (indeed, it is the negative version of) the so-called Closure Principle: “If I know that p, and I know that p entails q, then I know that q” — a principle that is definitely eminently reasonable, at first sight. The application to our case looks like this: If I know that I have hands, and I know that having hands entails not being a BIV, then I know that I’m not a BIV. But — says the skeptics — the consequent of this “BIV closure” is false, hence its antecedent must be false too: you just don’t know whether you are a BIV or not!

There are, of course, several responses to the skeptic’s so-called “closure denial.” Steup examines a whopping five of them: relevant alternatives, the Moorean response, the contextualist response, the ambiguity response, and what one might call the knowledge-that response. Let’s take a quick look.

A first attack against the BIV argument is to claim that being a BIV is not a relevant alternative to having hands; a relevant alternative would be, for instance, having had one’s hand amputated to overcome the effects of disease or accident. This sounds promising, but the skeptic can very well demand a principled account of what does and does not count as a relevant alternative. Such an account could perhaps deploy a type of approach naturally enough called relevance logic [10], but that would get pretty technical, so I’ll leave it for another time.

Second attack: G.E. Moore’s (in)famous “I know that I have hands” response. This is essentially an argument from plausibility: the BIV goes through if and only if its premises (I don’t know whether I’m a BIV, so I don’t know whether I have hands) are more plausible than its conclusion (I don’t actually know whether I have hands). Which, of course, Moore famously denied — by raising one of his hands and declaring “here is one hand.” But why, asks (reasonably, if irritatingly) the skeptic? To make a long story short, Moore’s counter to the BIV argument essentially reduces to simply asserting knowledge that one is not a BIV. Which, ahem, pretty much begs the question against the skeptic [11].

Third possible anti-skeptic maneuver: the contextualist response. The basic intuition here is that what we mean by “know” (as in “I know that I have hands,” or “I don’t know that I’m not a BIV”) varies with the context, in the sense that the standards of evidence for claiming knowledge depend on the circumstances. This leads contextualists to distinguish between “low” and “high” standards situations. Most discussions of having or not having hands are low standards situations, where the hypothesis of a BIV does not need to be considered. It is only in high standards situations that the skeptical hypothesis becomes salient, and in those cases we truly do not know whether we have hands (because we do not know whether we are BIVs). This actually sounds plausible to me, though I would also like to see a principled account of what distinguishes low and high standard situations (unless the latter are, rather ad hoc, limited only to the skeptical scenario). Perhaps things are a bit more complicated, and there actually is a continuum of standards, and therefore a continuum of meanings of the word “know”? [12]

Fourth: the ambiguity response. Here the strategy is to ask whether the skeptic, when he uses the word “know” is referring to fallible or infallible knowledge. (This is actually rather similar to the contextualist response, it seems to me, though the argument takes off from a slightly different perspective, and I think is a bit more subtle and satisfying.) Once we make this distinction, it turns out that there are three versions of the BIV argument: the “mixed” one (“know” refers to infallible knowledge in the premises but to fallible knowledge in the conclusion), “high standards” (infallible knowledge is implied in both premises and conclusion), and “low standards” (fallible knowledge assumed in both instances). Once this unpacking is done, we quickly reach the conclusion that the mixed version is actually an instance of invalid reasoning, since it is based on an equivocation; the high-standards version is indeed sound, but pretty uninteresting (okay, we don’t have infallible knowledge concerning our hands, so what?); and the low-standards version is interesting but unsound (because we would have to admit to the bizarre situation of not having even fallible knowledge of our hands!).

Finally: the knowledge-that response, which is a type of evidentialist approach. The idea is to point out to the skeptic that the BIV argument is based on a number of highly questionable unstated premises, such as that it is possible to build a BIV, and that someone has actually developed the technology to do so, for instance. But we can deny these premises on grounds of implausibility, just like we would deny, say, the claim that someone has traveled through time via a wormhole on the ground that we don’t have sufficient reasons to entertain the notions that time travel is possible and that someone has been able to implement it technologically. Yes, the skeptics can deny the analogy, but the burden of proof seems to have shifted to the skeptic, who needs to explain why this is indeed a disanalogy. Can someone please get me a red pill?

Now, why on earth did we engage in this, ahem, academic discussion? Because I wanted to give you a flavor of how philosophy makes progress, and why it isn’t particularly fruitful to compare it with progress in the natural sciences (did you see any systematic observation or experiment peeking through the above?). Indeed, I am writing a whole book on this topic, which I will hopefully deliver to Chicago Press by the end of the summer. No, make that I will definitely deliver by the end of summer…

The idea is that philosophy is concerned with exploring conceptual, as distinct from empirical, spaces, which is precisely what we have done above. Indeed, you could go through it again and try to build a concept map [13] to see whether you followed the discussion correctly and to visualize its unfolding. The five responses presented by Steup can be thought of as five peaks in the conceptual space defined by the BIV problem, with other possible responses having been examined and discarded during the long history of the debate (those would be conceptual valleys, to continue the metaphor). Not all peaks are necessarily of the same height — where the height roughly measures how good a given response is, and even the precise position and shape of the peaks may vary over time, as philosophers keep refining them in response to counterarguments from the skeptics.

Moreover, the metaphor should make clear that even to ask the question of what is the true answer to the BIV problem is, in a fundamental way, to misunderstand the whole process. If the BIV question were an empirical one — like “how many planets are there in the solar system” — then it would have one definite answer [14], and a bunch of bad ones. But in conceptual space there often are several reasonable ways of looking at a particular problem (“answers”), and it will not be possible to pare them down to just one. (Another way to put this is to say that conceptual space is wider than, and underdetermined by, empirical space.)

So, what should we then make of (academic) skepticism and its critics? I think the value of the skeptical position is that it fosters epistemic humility: we are really not as smart as we often think we are, and in fact we don’t even have unequivocal answers to very basic questions about knowledge. As for the responses to the BIV problem, the five sketched above represent peaks of different heights in the proper conceptual landscape, and in my mind the ambiguity and the knowledge-that peaks are significantly higher than the rest, the Moore response is the lowest, and the relevant alternative and contextualist options are somewhere in the middle. But I’m sure we can have a discussion about that.


Massimo Pigliucci is a biologist and philosopher at the City University of New York. His main interests are in the philosophy of science and pseudoscience. He is the editor-in-chief of Scientia Salon, and his latest book (co-edited with Maarten Boudry) is Philosophy of Pseudoscience: Reconsidering the Demarcation Problem (Chicago Press).

[1] In An Enquiry Concerning Human Understanding, published in 1748.

[2] A dictum, by the way, which can easily and rigorously be formalized in Bayesian terms.

[3] Here is the obligatory SEP entry, by Peter Klein.

[4] On Sextus Empiricus.

[5] Here is my take on Carneades.

[6] On Descartes’ epistemology.

[7] You can do this and much more by engaging the fun essays in the collection put together by Susan Schneider, Science Fiction and Philosophy: From Time Travel to Superintelligence, Wiley-Blackwell, 2009.

[8] Here it is, for your viewing pleasure.

[9] Epistemology, by Matthias Steup, SEP, 2005.

[10] Relevance logic.

[11] On George Edward Moore.

[12] I know, I know, this is beginning to sound rather Clintonesque. Then again, the former President of the United States did study philosophy at Oxford as a Rhodes Scholar…

[13] On concept mapping.

[14] Well, kinda. The famous “demotion” of Pluto to “dwarf planet” hinges on the rather arbitrary — and in some sense philosophical — question of what counts as a planet and why. Incidentally, and contra popular perception, it was Caltech astronomer Mike Brown who was chiefly responsible for killing Pluto, not my friend Neil deGrasse Tyson. Neil did, however, write a popular book about the story.

273 thoughts on “Are you sure you have hands?

  1. Hi Massimo,

    A very nice essay, and I’m pleased to say that I’m pretty much entirely in agreement with you, which makes a nice change from recent discussions!

    I would also choose the contextualist response or the ambiguity response, although I would probably lean more towards the former. I think Justified True Belief is a reasonably good definition of knowledge, Gettier problems only indicating that we might need to do a bit of work to clarify what counts as good justification. The word “justified” is to me a relative term: there is no clear threshold where we count justification as having been achieved. So it looks to me very much like we are dealing with a continuum. In particular I would make the point that there is pretty much nothing about which we can be absolutely certain, perhaps not even that 1+1=2, so I don’t really think that infallible knowledge exists. We can only have arbitrarily high confidence levels. The only way to make precise claims about knowledge is to make statements such as “I know with 99.5% confidence that…”, and this is not unlike what we do in science with statistical significance. So, to me, knowledge is not ambiguous (infallible or fallible) but vague (smeared over a continuum)

    Context certainly plays a role in shifting our expectations of the natural threshold of knowledge, but as you note it would be good to have a better theory of how this works. I propose two factors which might affect this threshold

    1) If we are explicitly entertaining a very far-fetched scenario, the threshold goes up.
    2) If we are entertaining a scenario which appears to be nonsensical, the threshold goes down

    My intuition regarding this particular example is that “I am a BIV” is far-fetched but not nonsensical. We can understand the claim and entertain the idea that it might be true. As such, the threshold for knowledge moves up and we feel we cannot claim knowledge that it is true or false.

    “I have no hands”, on the other hand, is a story without context. On the face of it, it seems to be contradicted by the evidence before us. Without an explanation of how it is that we are supposed to be handless, it is interpreted in the most obvious, natural way, and the claim appears to be nonsense. As such, the threshold comes down and we feel we do know that it is not true.

    Only when put in context as “I have no hands because I am a BIV” does the story make sense and now we can understand the claim and reinterpret the level of justification required. The claim now becomes far-fetched rather than nonsensical.

    If I’m right, then conflicting answers about what constitute knowledge is usually a product of ambiguity. Clarify the question and answers should be more consistent.

    However, when all is said and done, knowledge remains intrinsically vague, I feel I can simultaneously think that I know that I am not a BIV (meaning that I am quite justified in believing myself not to be a BIV) and that I don’t know that I am not a BIV (meaning that I am not justified in ruling out the possibility that I am a BIV). I don’t see this as a major problem as we deal with vague terms all the time. Is a grain of sand small? Yes, if we’re in the context of comparing it with beach balls and buckets, but no if we’re comparing it with molecules of silicon dioxide.


  2. Hi Massimo,

    … did you see any systematic observation or experiment peeking through the above?

    Well, since you ask, yes I did! If fact I think that BIV scenarios are best analysed by the scientific method. We all have a stream of sensory data coming into us, and we construct models to explain and understand that stream of sensory data. The scientific method then tests them for explanatory power and predictive power.

    The BIV model has little explanatory power. You have to postulate a heck of a lot (both the vat and the brain) with no explanation at all about why they got there. The entire real-world-simulation that is part of the BIV model has to be taken by fiat (or, if you then want to postulate why we are a BIV, with that particular simulation, then one has to postulate a heck of a lot beyond the mere BIV). Overall it is horribly, horribly unparsimonious.

    By contrast the “normal world” model is vastly more parsimonious, all you need are a couple of quantum fluctuations in the early universe and everything follows from that. The amount of information that needs to be input to specify the basic physics of this world is vastly, vastly less.

    As for predictive power (by which I mean predicting future aspects of the sensory data stream), the BIV has zero. At least, it does so unless you make all sorts of assumptions about who created this BIV and why, and, by definition, you have zero evidence for any of that. Thus, since we would never know why we are a BIV, the model has zero predictive power.

    The “normal world” model actually has a vast amount of predictive power, as we know from the fact that engineering works, and planes we build fly, and predictions we make for solar eclipses come true.

    One could, of course, try to build the whole “normal-world” model into the BIV model, in order to gain its expanatory/predictive features, but then the BIV becomes simply a useless and superfluous add-on to a good model, and thus is excised by Occam.

    So, overall, the scientific method gives a straightforward account for strongly prefering the normal-world model over the BIV (though of course scientific accounts are never certain in an absolute sense).


  3. Coel,
    The scientific method then tests them for explanatory power and predictive power.
    Some consistency in your arguments is called for.
    You have recently argued strongly that
    1) science answers moral questions (unproven and logically incoherent),
    2) the multiverse is a scientific concept (untestable and unproven),
    3) semantics can be derived from syntax (unproven and logically incoherent).

    And yet in all cases these ideas have not survived scientific tests and there is thus no useful predictive power. The belief in the power of science is not an idea you can pick up and discard at will. It must be applied consistently otherwise you open yourself to accusations of, at best, confused thinking, and at worst, dishonesty.

    I suspect you have missed an essential point of Massimo’s post, and that is the need for epistemic humility, something that is lacking in your dogmatic assertions about unprovable and open disputes.
    Massimo referred to Sextus Empiricus. Here is a book I recommend for your reading – Sextus Empiricus: Outlines of Scepticism, edited by Julia Annas and Jonathan Barnes( Yes, I have the book. This is another book for you to add to your already long reading list 🙂 In it you will discover that Sextus Empiricus talks about the five and ten modes of suspension of judgement (Book 1 page 40).

    I don’t recommend anything nearly as radical as their modes of suspension of disbelief. But I do mention it as an important caution for epistemic humility, something that modern skeptics are sorely lacking.

    See especially this SEP article on wisdom ( which discusses, among other things, the place of epistemic humility in wisdom. See section 5, Deep Rationality Theory.


  4. Hi labnut,

    You have recently argued strongly that
    1) science answers moral questions (unproven and logically incoherent), …

    Yes, and it’s true. And you’re welcome to re-hash this again, but if you do so please would you actually engage with my replies?

    2) the multiverse is a scientific concept (untestable and unproven),

    Yes, the multiverse is indeed a scientific concept, and the concept is testable (though it has not yet been proven).

    3) semantics can be derived from syntax (unproven and logically incoherent).

    No I did not say that. What I said is that there are no such things as zero-meaning, syntax-only statements.

    And yet in all cases these ideas have not survived scientific tests and there is thus no useful predictive power.

    That is simply not true.


  5. Hi Labnut,

    I think it’s important that Coel and I simply have very different intuitions about these questions than you do, so where you think Coel is confused or dishonest, I don’t think either is fair (and nor, I’m sure, does Coel).

    Let’s acknowledge that communicating ideas clearly while engaging in these debates is quite difficult and restrain ourselves from throwing accusations of obtuseness at each other.

    It might be best to save the specifics of these arguments to future topics more relevant to them.


  6. Given all the discussion of physics and the scientific method and prior posts this video is a good example of how problems are worked through – Is Our Universe Part Of A Multiverse? – Professor Alan H. Guth –

    How would discussions of language meanings/philosophy come into play?


  7. Coel,
    That is simply not true.
    I suspect you don’t appreciate the meaning of the concept of epistemic humility, given this categorical denial.

    You make this dogmatic assertion in the face of the fact that important thinkers have come to the opposite conclusions. Massimo, for example disagrees with you about assertions (1) and (3) and these are his fields of expertise. Peter Woit is certainly an expert as are Lee Smolin and Jim Baggott. They disagree categorically with your claims about the multiverse, assertion (2).

    Thus you dogmatically assert your position in the face of important disagreement by some experts in the relevant fields. Moreover you make these assertions in the absence of evidence. That does not qualify as epistemic humility.

    You probably claim you are a skeptic. In that case let me remind you that epistemic humility is an essential feature of honest skepticism. Skepticism is not a tool that you turn off where your own ideological predispositions are involved and then turn on to attack different beliefs. That is plain opportunism. Skepticism is an equal opportunity predisposition that is applied with unsparing honesty to all beliefs, not just to your disbeliefs

    The point of my preceding and present comment is not to argue the truth/falsity of assertions (1), (2) and (3) but rather to point out that 1) there are important disagreements about them, on the part of experts, and 2) your arguments were found to be rather unconvincing by some experts.

    In that case the only reasonable position is one of epistemic humility, that is, if you are a skeptic. You might of course claim you have superior knowledge that outranks that of all the experts. But you have failed to demonstrate that knowledge and you will thereby certainly demonstrate your lack of epistemic humility, that essential characteristic of honest skepticism.


  8. DM,
    see my reply to Coel, above, where I argue that this is essentially about epistemic humility. Additionally, I assert that epistemic humility is an important aspect of honest skepticism.


  9. Interesting essay, even though my first thought was that the detractors of philosophy (and I’m thinking the scientists among that crowd) will say “Who cares?” regarding the BIV argument as it’s not at all relevant to what we are doing on a day to day basis nor does any scientist takes it seriously when doing their work. I don’t agree with that perspective but I’d be curious as to what your response would be to that Massimo? It seems me that aside from the criticism that philosophy does not contribute anything, there is a further criticism that philosophy studies things that are essentially navel gazing and not worth having academic discussions on.


  10. Coel, where did you see in Massimo’s post an observation or experiment? I reread his post and can’t find it in there or in your response here.

    To me, Massimo is analyzing the hypothetical situation in which we could be a BIV and would not know it because all of empirical reality is part of the BIV. No scientific study of this subject matter will get rid of the BIV argument here as all empirical findings would be part of the said BIV. I don’t think it’s likely that we are in BIV but at the very least, we can’t say with certainty that we are not. I think of this in terms of Bayesian priors, which maybe very low for BIV but not 0%.


  11. Hi labnut,
    A couple of responses. First, you are very keen on this meta-arguing, but then shy away from actually engaging in the substance of the discussion. Second, it seems to me that your main method of arguing is to ignore what someone has actually said, and then make a whole set of accusations, such as that I am being inconsistent. You are routinely derogatory about others, for example suggesting that I lack curiosity simply because I don’t jump to put your choice of book ahead of mine on my reading list. Third, you repeatedly ignore what I say and make no attempt to engage with my actual answers. For example, here you suggested that I was making claim 3; I replied explicitly saying that I was not, and then you reply again as though I were making claim 3. Fourth, on epistemic humility, you are as guilty as anyone of making grand claims. Fifth, on experts, I can quote plenty of people who agree with me, just as you can quote people who do not (in any case it’s the arguments that matter). Sixth, it’s the arguments and the truth of the matter that interest me, any chance we can concentrate on those rather than having these diversions into meta-arguments?


  12. imzasirf,

    No scientific study of this subject matter will get rid of the BIV argument here as all empirical findings would be part of the said BIV.

    Science is not only about empirical data but about model building from those data. At that stage the BIV is rejected as the far worse model using principles of explanatory and predictive power and parsimony, excising information from the model that does not explain anything. That is an entirely scientific approach (see my first comment on this thread for a longer exposition of both).

    I don’t think it’s likely that we are in BIV but at the very least, we can’t say with certainty that we are not.

    See the last line of my above comment for me saying exactly that, from a scientific perspective.


  13. I think we agree on the conclusion but I don’t think it’s science that gets us there as generally understood.

    You use examples like explanatory and predictive power here to compare the BIV with presumably scientific models of the world but this is missing the point of the example. A world where there is a BIV and no BIV would have the exactly same scientific models work just as well. The question is, can ever know whether we are BIV or not? That is not something any new scientific model would provide us as the BIV proponent can always come back and say “well that scientific model is within the BIV”.

    To object to this BIV view requires analyzing the situation conceptually or philosophically to see if it’s reasonable for us to believe in BIV. What are we entitled to believe beyond the empirical data if anything? Maybe we leave a slight chance for BIV to be true but consider it largely unlikely. It’s certainly not logically impossible.


  14. Massimo, since you’re referencing Hume, based on his own comment about his being asked how he could sleep at night if skeptical ideas, especially on induction, etc., were all true, and he said that he basically slept like a baby, I would postulate a sixth, even more psychological response: The “act as if response.” That said, a Dan Dennett might torpedo it as being a potentially unsound statement of folk psychology.

    That said, my thoughts on a couple of the five responses as outlined by Massimo:

    Option 3, the contextual option? Agreed. And, in both here and option 4, one could move beyond “high” and “low” standards into the edges of multivalued logic by taking stabs at percentages of certainty of knowledge. Of course, a Pyrrhonic skepic will entirely reject that endeavor, while an Academic might lead us on an infinite regress by questioning by what standards we can claim to make judgments on the percentages of likelihood that we offer up, or even on more vague “high” vs “low.” A Pyrrhonist then might say, “See, that’s why we reject that whole prospect and enterprise.” (Nice basic intro to Carneades, BTW.)

    Option 5, the “knowledge that” option? You reject it on scientific grounds, not philosophical ones. False move. A BIV is logically possible. Even granted the philosophical validity of “conceptual spaces,” in something like a simple, classical formal argument, IMO, such spaces should be grounded in philosophy, not science.


  15. The concept of knowledge has two sides; The knower and the known, or if you prefer, how we know and what we know. Otherwise referred to as the consciousness and the physical.
    The issue of consciousness is a very open question, but then so is the basis of the biology from which it arises. Possibly we could assume these two issues are fundamentally connected and biology is inherently conscious. Not only might it explain some of the features of biology, such as why it is so tenacious, but would also help to explain the nature of consciousness, since biology is bottom up, yet our conscious perceptions are effectively top down. We see form, yet are motivated by energy.
    It should be noted that the western religious convention of monotheism considers the spiritual absolute as an ideal, yet the physical absolute is basis. The state/universal equilibrium from which form arises, while an ideal is largely a collection of preferred features.
    So logically a spiritual absolute, the source of this consciousness, would be the essence of awareness from which we rise, not an ideal form from which we fell. It does happen to be politically convenient for those managing society to assert their ideal as an absolute.
    Now there are limits as to how far we might be able to, or even want to probe the depths of this awareness, as most people quickly loose their bearings away from those conceptual benchmarks they take for granted. Think for a moment if you were to loose the form and structure of language.
    Yet language does arise from more primordial reflective abilities. For instance, we easily distinguish between noun and verb; object and action, yet realize that there is no clear line between the two. Yet we do mull over this extensively. Consider the uncertainty principle; that you can’t know both the position and momentum of a quantum object. The reality is this applies to everything. A moving car does not have an exact location, or it wouldn’t be moving.
    Which then goes back to the question of knowledge. What do we know? Do we know objects/form/noun, or do we know action/energy/verb?
    Consider a particle accelerator; We take two (presumed) objects and strike them against each other. Form-action-interaction. It could as well be light striking our eyeballs, that had previously bounced off some other form, thus giving information derived from that previous encounter, just as those ions give up information they had been carrying.
    So the objects are essentially nodes in networks of interaction. And even then we could view the carrying entities as the nodes and the information as an effect of the network, or we could view the information as digital nodes to be extracted from the network of noise from which it emerges.
    In the Evidence Crisis thread I made the argument that since we individually experience change as a sequence of encounters and events, we think of time as the present moving from past to future, when the reasonable argument is that those encounters are occurring and dissipating, thus it is actually the events going future to past and so time is an effect of action, similar to temperature. That we are effectively a molecule in a thermal medium and are just bouncing/trading energy around.
    This makes time equivalent to frequency and temperature to amplitude. Since we are as individuals, a thermal body, existing in that thermal medium, much of what we process intellectually is thermal, which we refer to as emotion and intuition. The rational side of the brain orders these observations and impulses into the sequence of events we individually experience as memory and collectively as history.
    This distillation of the narrative from the non-linear medium explains a lot of the disconnects, biases, pre and post assumptions, etc, that make our perception of reality seem distorted and occasionally distinct from other points of view.
    Yet without that linear perception holding all those events together, however confusing, we would have no memory. Much like an infant is as obviously aware as any adult, butit does not yet possess the ability to process this information in a way to effectively store it and thus has no memory.
    Now many of these events and encounters we experience as reality don’t seem tangible when viewed from other points of view and so the questions of their nature rise to the surface. Is ‘reality’ real? Maybe we should look at it the other way around; What is this ‘real’ we take for granted? A diamond is quite real, yet so is a soup bubble. Now some of our thoughts, experiences, insights, observations, etc. do seem like diamonds, especially when lots of other people agree they sense the same effect. While some definitely fall in the soap bubble category. A pretty little flash of perception, like a spark from a fire, radiating its energy and gone, only seen and sensed by ourselves. Then again feedback loops frequently fire through groups of people and that belief so widely held, turns out to be another, larger soap bubble.
    The energy which manifests these forms is real and the forms themselves are real, yet that energy is action. It creates and dissipates forms. Some have lots of energy, yet burn though it really fast, so high amplitude, rapid frequency. While others might have much less energy, yet sustain it for long periods.
    As individual people, we live and burn similar energies and durations. Some of us blow up big bubbles and some little bubbles. Some are parts of other bubbles. Some poke holes in bubbles.
    That’s how I see reality and now lunch break is about over.
    John B. Merryman


  16. Hi imzasirf,

    A world where there is a BIV and no BIV would have the exactly same scientific models work just as well.

    If the BIV duplicated every part of the normal-world model, plus added on the BIV stuff, then the BIV stuff is superfluous, it adds nothing to the explanation, and is excised by Occam’s razor.

    What are we entitled to believe beyond the empirical data if anything?

    Empirical data never tells you anything by itself (other than, perhaps, a photon arrived at such-and-such a time from such a direction, another one arrived …, etc). Everything beyond a list of photon-arrival events is a model, and in constructing that model science uses principles of parsimony and explanatory and predictive power.

    as the BIV proponent can always come back and say “well that scientific model is within the BIV”.

    This is equivalent to a choice between (1) real world, and (2) real world plus invisible pink unicorns which have no effect whatsoever on any sense data.

    Given that choice science picks the former, dismissing the extra unicorns as useless and superfluous. By the same token, if the BIV is simply a “real world plus …” proposal then the unevidenced additions are excised by Occam. This principle of picking the most parsimonious proposal that explains all the data is a standard part of the scientific method.

    (If anyone wants a justification for that I wrote one one here)


  17. I guess the problem some of us might have with Coel’s initial comment to Massimo is why he sees a compelling need to make it. As has been pointed out in other comments, Massimo’s point is to clarify what is meant by conceptual space, as opposed to empiric space, and to show it in action.

    The question in my miind is, given this sort of conceptual problem, and the epistemic uncertainty that Massimo sheds on it, why one would even pursue it to along the lines that Coel seems to suggest would be appropriate.


  18. Hi Thomas,

    … with Coel’s initial comment to Massimo is why he sees a compelling need to make it. As has been pointed out in other comments, Massimo’s point is to clarify what is meant by conceptual space, as opposed to empiric space, and to show it in action.

    The “empirical space” is utterly riddled with concepts. The view that science is merely about empirical data, and not concepts, is totally untenable (unless you’re happy with no more than a list of sensory photon-arrival events). Thus one cannot have any such neat divide between “conceptual space” and “empirical space”. Thus, some of the things that might be considered “philosophy” are actually things that science deals with routinely.


  19. Coel,
    that is what I call a non-response response.

    So let’s retrace our steps and I will show you the relevance of what I said.

    The very first word that Massimo used in the post was the word ‘skepticism’. That set the scene and the broad subject. He went on to quote David Hume’s famous dictum to illustrate what he meant by skepticism:

    In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. A wise man, therefore, proportions his belief to the evidence”.

    This is epistemic humility, ‘proportions his belief to the evidence‘ and it is an important part of skepticism, as illustrated by David Hume’s dictum.

    You claimed “The scientific method then tests them for explanatory power and predictive power.”, which of course is perfectly true within the empirical domain.

    I then pointed out the inconsistency in your arguments where you have made categorical assertions about three subjects that have little or no evidence. And therefore I argued more epistemic humility was called for, not your categorical certainty.

    I made the important point that skepticism is an equal opportunity predisposition that is applied with unsparing honesty to all beliefs, not just to your disbeliefs. This of course is exactly the point of people like Sextus Empiricus(which is why I recommended his book).

    This is the great failing of modern skepticism, it is only applied to targets of opportunity and I was using you as an example of that. You exempt your pet beliefs from the tests of skepticism whereas rigorously honest skepticism would subject all beliefs to the same critical examination.

    Let me repeat again. I regard the failing of modern skepticism as its inability to apply the tool of critical examination with unsparing honesty to all their beliefs and not just their disbeliefs. I listed your three claims as a perfect example of what I mean. One might call it skeptical bias, which is anathema to the true spirit of skepticism.


  20. Coel,
    The view that science is merely about empirical data, and not concepts, is totally untenable
    That is not what Thomas said. Why do you attribute this statement to him? Would you like to quote his words?


  21. Hey Coel,

    I don’t disagree with anything you said in your reply to Massimo’s article, but I suggest you are missing his point. The point I got was that, even though it may not be the best way to approach reality, there is value in (at least some people, specifically, philosophers) spending time and effort to consider these other scenarios. In this case, the value is “epistemic humility”.



  22. There’s no need to take a defensive position when you’re not being attacked. But your point regarding a “neat divide” perhaps goes to the heart of the matter that perhaps others, like Massimo, might want to weigh in on. Statements like, “Thus, some of the things that might be considered ‘philosophy’ are actually things that science deals with routinely” are to my mind not responsive to the point of the post. My problem is with what seems the ideological nature of your response.

    Your grocery cart is blocking the aisle while other shoppers want to shop too. I’m not even sure I fully understand a statement like “The ’empirical space’ is utterly riddled with concepts.” Who riddled those empiric spaces with concepts? I don’t think I said that science is “merely” about empiric data, not concepts. I don’t really think I have an agenda in mind. But, if you think that I am skeptical about whether branding something as scientific as opposed to philosophic makes for a clear demarcation, you are correct.


  23. There is another version of the skeptical argument, which renders responses like Cole’s un-useful.

    Any justification for the existence of the external world must come from our senses, but appeal to the senses as justification presupposes the existence of the external world. Thus, the existence of the external world stands without warrant.

    This is at the heart of the I,II,II argument, as posed by Crispin Wright in his “Facts and Certainty.”


  24. Hi Aravis,

    That argument doesn’t quite seem to work, at least as you put it. I think we can be relatively certain that we experience things, and the external world can be seen as the hypothesis that best explains these experiences. I really don’t get where the justification presupposes the existence of the external world.


  25. There are only senses (and sense organs), if the external world exists. Thus, appeal to those organs and their processes cannot justify the belief in the existence of the external world.


  26. Hi five on the “act as if response,” SocraticGadfly, an explanatory approach that I find myself more drawn to as I age. But, gee, I thought it was mine . . . as if. Thanks for the reminder that there are others out there with similar thoughts. It is is not easy to explain, but timely and appropriate here.


  27. Hi Massimo,

    A sense is what tells you about the external world, which is why Aravis calls the argument from senses circular. But not all experiences are sensory. For example, Descartes’ demon could be making you hallucinate.

    Are you saying that you agree with Aravis that inferring that the external world exists because of what we sense is circular?


  28. Pick up any elementary epistemology text and you will find that the “inference to the best explanation” justification for the external world has been nearly universally rejected, as question-begging, at best.

    Experience of the external world is via the senses and the senses only exist, if the external world exists. Thus, appeal to the testimony of the senses cannot justify the existence of the external world, because they presuppose its existence.

    Pretty straightforward. And quite devastating. This is why the skeptical challenge is, you know, hard.


  29. For what it’s worth, it is my view that the skeptical arguments are unanswerable, for they speak to the very relationship between evidence and empirical judgment and the presuppositions entailed in that relationship.

    It is for this reason that in my own work, I have embraced what I call a “common sense naturalism”, grounded in the naturalistic reading of Hume (via Norman Kemp Smith), the philosophy of Thomas Reid, and the later Wittgenstein, especially of “On Certainty”. This approach rests on rejecting the skeptic’s demand for universal warrant and prioritizing belief over reason. I’ve worked some of this out, in the following articles, both published in the journal, Philosophical Investigations:


  30. Hi Aravis,

    Sorry, I don’t buy it, at least not based on your account. You might be right about what’s in the literature, but I have too much of a backlog of reading material to go through it for myself if you’re not interested in debating the argument here.


  31. DM,
    Perhaps it’s not that we are virtual simulations in a super computer made by some advanced civilization, but that we are physical assemblies (programmable matter) output from a super 3D printer (matter compiler) made by some advanced civilization.

    Doesn’t that make more sense than being a simulation. 🙂


  32. Not sure what is there to “buy.” The argument is pretty straightforward, and exceedingly solid. You just don’t want to give up the scientistic ghost and accept that a purely philosophical argument is, in fact, empirically (i.e., scientifically) unassailable.


  33. Hi Massimo,

    DM, hallucinations are mistakes of the senses. That was Descartes’ point.

    Perhaps. Descartes’ point is not my point.

    I think the external world exists and I think this belief is warranted.

    It seems that there are two ways of thinking about whether senses (or hallucinations) could exist without an external world. I think they could. You think they could not. Either way, I think belief in the external world is warranted.

    If I concede your point, then I can only have senses if the external world exists. Since I have senses, it follows trivially that the external world exists and my belief is warranted.

    If I do not concede your point because I might be a BIV or because there might be a demon tricking me, then my belief is still warranted because it is the best explanation on the grounds of parsimony.


  34. DM, wrote:

    “Not all experiences are sensory. For example, Descartes’ demon could be making you hallucinate.”


    But this is exactly Descartes’ point. Because genuine and imagined experience are indistinguishable “from the inside,” one cannot tell, just on the basis of that experience, whether one is experiencing the external world or not. Thus, the belief that there is an external world is unwarranted, in the absence of some independent criterion.


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