The Hocus Pocus of Radical Skepticism

by Alexandre Couto de Andrade

Human beings have a limited capacity to apprehend reality. Our senses are limited and we are incredibly prone to self-delusion and cognitive biases. For this reason, critical thinking and a healthy dose of skepticism are fundamental tools when it comes to understanding the world we live in. Radical skepticism, however, is much of a problem.

Radical skeptics claim that we cannot be sure of anything at all. Such an affirmation is completely detached from our daily experience. There are apparently many things that we can take for granted. There seems to be a physical world that is independent from the internal states of our brains. How can they deny the existence of animals, plants, planets, stars, other human beings, cities, oceans, etc? Even if we admit that these things are not exactly what they seem to be, we can still be sure that they do exist. So, how can radical skeptics support their arguments? I will now explain how they do it, and try to show that their claims are completely irrelevant.

Epistemology defines knowledge as “justified true belief”, i.e.:

1 – Knowledge requires truth, because you cannot not know something that is not true. For example: you cannot know that a circle is square.

2 – Knowledge also requires belief, because you cannot know something that you do not believe to be true. For this reason, a statement like “I do not believe in witches, but I know that they exist” is absurd.

3 – Knowledge requires justification, because to believe something you must have reasons to think that it is true.

Radical skeptics argue that knowledge is impossible because we cannot know the truth. The following text is an extract from the Stanford Encyclopedia of Philosophy, that explain how they try to corroborate this claim:

According to [radical] skeptics, the limits of what you know are narrower than you would like to think. There are many things that you think you know but actually fail to know. For example, you think you know that you have hands, but in fact you don't. How can the skeptics expect you to take such a strange conclusion seriously? Here's how. As a first step, the skeptics will focus on another proposition, about which you are likely to agree that you don't know it. As a second step, they will get you to agree that, since you don't know that second proposition, you don't know the first one either: the proposition that you have hands.

When the skeptics get their argument started with some other proposition about which you are likely to agree you don't know it, what do they have in mind? They direct your attention to what is called a skeptical hypothesis. According to a skeptical hypothesis, things are radically different from what you take them to be. Here are several examples:

• I'm lying in my bed dreaming.
• I'm deceived by an evil demon.
• I'm a mere brain-in-a-vat (a BIV).
• I'm in the matrix world.

What the skeptics will point out, and what they think you will easily agree with, is this: For any particular hypothesis on the list, you don't know that it is false. This works better for some than for others. It works really well for the BIV hypothesis (...). The idea is that, if you are a BIV, you are reduced to a mere brain which is stimulated in such a way that the delusion of a normal life results. So the experiences you have as a BIV and the experiences you have as a normal person are perfectly alike, indistinguishable, so to speak, "from the inside." It doesn't look to you as though you are a BIV. After all, you can see that you have a body, and you can freely move about in your environment. The problem is that it looks that way to a BIV, too. As a result, the evidence you have as a normal person and the evidence you have as a BIV do not relevantly differ. Consequently, your evidence can't settle the question of whether or not you are a BIV. Based on this thought, the skeptics claim you don't know that you are not a BIV. That's the first step of the case for skepticism.

Let us now focus on the second step. The basic thought is that, if you don't know you're not a BIV, you don't know you have hands. That thought is extremely plausible. After all, if you are a BIV, you don't have any hands. So if you can't distinguish between being and not being a BIV, you can't distinguish either between having and not having hands. But if you can't distinguish between having and not having hands, surely you don't know that you have hands. Putting the two steps of the skeptic's reasoning together, we get the following argument:

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. Therefore:
3. I don't know that I have hands.

Of course, few radical skeptics would really argue that we actually are brains in vats. Our reality is so overwhelmingly complex and internally coherent that it would take the powers of a god to simulate it. This is just an allegory to make their point. Interesting, but irrelevant.

Just for fun, I will try to show that if you are a brain in a vat (BIV):

1. The fact that you are a BIV is absolutely irrelevant for every practical purposes;
2. In your BIV reality (BIVR), there are statements that are true;
3. Due to (1) and (2), knowledge is possible, regarding at least some relevant matters, even if you are a BIV.

1 – Irrelevance argument:

If you are a BIV, your BIVR has some properties:

1.1 – It is absolutely impossible for you to know whether or not you are a BIV;

1.2 – It is absolutely impossible for you to change your condition or escape your BIVR.

1.3 – Even though it is illusory, your BIVR is extremely complex and internally coherent.

First of all, let's analyze the implications of statements (1.1) and (1.2): If your condition is unknowable and ineluctable, why should you even wonder if you are a BIV? It makes no difference. No questions will be answered, no conditions will be changed. Do not waste your BIVR time!. Enjoy it, instead! Explore your amazingly complex BIVR. Make lots of BIVR friends, listen to good BIVR music, travel to as many BIVR countries as you can, eat BIVR food, have BIVR children, read BIVR books, learn BIVR science... In short, live your BIVR life! It is the only one you will ever know!


2 – In your BIVR, there are statements that are true:
Truth is not independent of context. Consider the statement: “Most people are Chinese”. If we are talking about the whole world population, that is not true. But if we are talking about people who live in China, it is true. Similarly, in the context of your BIVR, there are statements that are true. For example: “the BIVR Earth orbits a BIVR Sun”;  “a BIVR triangle has three BIVR sides”.

3 – Knowledge is possible regarding at least some relevant matters:
From (1) and (2): regarding at least some relevant matters, knowledge is possible.