Putnam’s Minotaur

Let us explore the labyrinth of a fascinating thought experiment. But as it is with all labyrinths there is a Minotaur at the centre. One maybe a bit more interesting than a first glance might suggest.

Formerly, I, Zhuang Zhou, dreamt that I was a butterfly, a butterfly flying about, feeling that it was enjoying itself. I did not know that it was Zhou. Suddenly I awoke, and was myself again, the veritable Zhou. I did not know whether it had formerly been Zhou dreaming that he was a butterfly, or it was now a butterfly dreaming that it was Zhou. But between Zhou and a butterfly there must be a difference. This is a case of what is called the Transformation of Things.

Part I

In which a stale science-fiction cliché is introduced

Have you heard of the “brain in a vat” (BIV) scenario? Chances are you have — After all it has become the basis for a multitude of thought experiments. The film “Matrix” is perhaps the most notable example, cementing BIVs place as science-fiction trope.

If you haven’t guessed it already, this is the scenario: Imagine your brain was removed from the rest of your body, connected to a life-support system as well as another machine. This machine would send your brain the same electrical impulses it receives when experiencing the world in its flesh suit. Ultimately this contraption would simulate an internal world indistinguishable from what the brain normally perceives.

Now that we have that out of the way, let’s take a look at what Hilary Putnam wrote on it. Which is not only a beautifully elegant argument, but also opens the door to a quite terrifying scenario. And no, that scenario is not “We are brains in a vat”.

Part II

In which neither brains nor vats make an appearance

Following is a simplified explanation of the argument Putnam made in his[1] book “Reason, Truth and History”. It’s a well-written treat and I highly recommend reading it.

The cornerstone his argument builds upon is — very simplified — this: We refer to an object via a sign. This is only possible if the signs signifier has a causal connection to the signified.

At first this may seem cryptic, but bear with me as we take a brief excursion into some light semiotics. Do note that these definitions are in no way complete and only cover the bare minimum we need for our purpose.

  • An object can be anything imaginable. Putnam however restricts this in his book to “Something that actually exists (i.e. not just an ‘object of thought’)”.
  • A sign is the composite of two things: The signifier is the form a sign takes, and the signified is the object it represents. For example together the word “tree” as signifier, and the concept of a physical tree as signified form a sign.[2]

Now that was simple enough, but what is this elusive “causal connection” we require? Well, that’s something Putnam never defines, instead writing extensively about what it is not[3]. For the sake of brevity here’s the rundown:

A signifier has no intrinsic connection to the object it designates. The word “tree”, as well as any mental or physical images of a tree do not by themselves represent a tree. All of these can only refer to the concept of a tree if there already is some form of causal relationship that links both together.[4]

With all that groundwork finished we can now finally get to the meat of Putnam’s argument, and gain closure about our status of disembodiment.

Part III

In which we finally see the poodle for his core

Before anything else it should be stated that Putnam’s argument is just this: An argument. The BIV thought experiment is of course far from completely explored, and there is no definite answer to the posed question. That said, let us now delve into what this fellow said about that thing.

  1. The BIV scenario proposes a situation in which sentient brains are placed in vats and through a device are stimulated in a way that they experience an internal world (IW) indistinguishable from the external world (EW) in which they are kept in a vat.
  2. If that is the case, then any experiences and words, images and thought produced by these brains would refer to objects in the IW exclusively. For example if a BIV were to experience, imagine, or talk about a tree it would refer to the object in the context of the IW. As the BIV has no causal connection to trees in the EW, the sign “tree” can only represent the concept of trees as they exist in the IW.
  3. Thus if a BIV formulated the thought “I am a brain in a vat” every sign in that thought — brains, vats, being something — could only refer to an object in the IW.
  4. For the statement “I am a brain in a vat” to be true or even meaningful in the context of the EW it needs to be made in that same context. Due to a lack of causal connection a BIV is not able to make that statement in that context.
  5. It concludes that we are not BIVs as a BIV can not formulate the thought “I am a brain in a vat”.

Part IV

In which we stubbornly refuse to not be imprisoned by aliens

Strange is the night where black stars rise, And strange moons circle through the skies, But stranger still is Lost Carcosa.

This is the point at which almost everyone goes “But what if we are BIVs? What if the EW is in every regard so very similar that the premise our thought is reasonably translatable to that context?”

First, let me say that this is indeed possible. There’s nothing in Putnam’s argument that excludes this possibility. But it doesn’t invalidate the argument either. A sign in the IW still only refers to an concept in the IW, no matter how similar it might be in the OW.

Additionally, and much more importantly consider that this train of thought is boring. If, in fact, we are something akin to a BIV, but are unable to formulate it, then what form might an external world take?

What if we suddenly find ourselves not in Kansas anymore? What eldritch horrors could haunt a plane so alien it is beyond even our imagination? A plane that might not even have the familiar concepts of space, of time, of identity? How do you open your eyes to something that lies so far outside your comprehension?

So it is that Putnam’s argument closes one door and opens another. And that is what makes it so fascinating: Not the conclusion, but what lies beyond it. After all nothing is more stimulating to our imagination than something unimaginable.


[1]: “Hilary”/”Hillary” is indeed a unisex name, in case you were wondering. And there’s nothing wrong with that. It means “cheerful, happy” :).

[2]: This is according to Saussures “dyadic” model. Peirces “tryadic” model along with other more modern ones are in much wider use today. However, the dyadic model is quite sufficient for our purposes.

[3]: Which makes sense considering his argument doesn’t need the minutiae of a causal connection workings, it only needs to prove that there can’t be one under certain conditions.

[4]: If this seems illogical, I suggest reading the source text. Putnam’s arguments are sound, but this text is already long enough without rewording them.