Essaykonkurranse 2023: Andreplass

Vi gratulerer Rasmus Moldstad Bakken for andreplassen i Forum for Psykologi og Filosofis essaykonkurranse! Vår begrunnelse lyder som følger: “Kan vi egentlig vite noe om andres opplevelse? Hva om «alle andre» bare er et resultat av en overbevisende simulasjon? I følge de som i filosofien kalles skeptikere er svaret nei, vi kan ikke vite. Denne teksten forsøker å argumentere mot skeptisisme, og på den måten styrke psykologiens antakelse om at intersubjektivitet er mulig, altså at det er mulig å vite noe om andres indre tanker og følelser. Teksten presenterer (om enn kompliserte) argumenter på en klar og strukturert måte, og er et interessant eksempel på hvordan filosofi kan brukes for å underbygge eller svekke påstander i det psykologiske fagfeltet.”

Nedenfor følger teksten

A Defence of Intersubjectivity through Modal Logic

By Rasmus Moldstad Bakken

1    Introduction

In this essay, I will argue that we can know that other people think the same way that we do. In other words, I will argue that we can know that the claim of intersubjectivity is true. I will first present a skeptical argument against this claim, which says that we cannot have any knowledge of the external world and in particular cannot know if the claim of intersubjectivity holds. Then I will reformulate this claim in the framework of modal logic. Subsequently, I will use the framework of modal logic to refute the skeptical claim and hence conclude that it is possible to know that the claim of intersubjectivity is true.

This question should be interesting from both a philosophical and a psychological point of view. For the philosopher, battling the skeptic has been an endeavor lasting several thousand years, and so another argument against them should be cherished. For the psychologist, if it turned out that the skeptic was right and we could not know that other people think the same way we do, then this would cast serious doubt on the methods and practices developed in their field. In a world where everyone else is a robot, surely no fruitful psychology can be achieved.

2    The Skeptical Scenario

The skeptical argument is an argument for the thesis that humans know very little. We know so little, in fact, that we do not have any knowledge of the external world. Hence, one such thing that we do not know is that the claim of intersubjectivity is true. This means that we cannot know that other people, that we interact with on a daily basis, actually are human beings in the same sense that we are. The skeptic will argue that we cannot know that other humans think the way we do. For all we know, according to the skeptic, the human beings we interact with could be robots.

How does the skeptic defend such a view? It is the skeptical scenario that does all the philosophical heavy lifting. The skeptical scenario goes as follows. Imagine that a crazy scientist kidnaps you tonight, whilst you are fast asleep. They drag you into their laboratory and connect your brain directly to a supercomputer using all sorts of fancy scientific equipment. When you wake up tomorrow morning, everything will seem ordinary to you. You will experience waking up in your own bed, making yourself a cup of instant coffee that doesn’t taste too good, and be on your way to another semi-exciting lecture about Freud. However, this is all a simulation. The mad scientist’s supercomputer is simulating all your experiences. Hence, when Professor Hovet stops you after class to ask some concerned questions about your latest essay, it is in fact the supercomputer you are talking to and not an actual person.

How does this pose a problem for your knowledge of intersubjectivity? Well, the skeptic will argue that you could never distinguish the conversation you have with Professor Hovet in the simulation and a potentially similar conversation you have with them in the real world. The simulation is so good that there are no external signs that you are actually talking to a supercomputer. So, if you are of the belief that other people think the same way you do, then you will be wrong in the first scenario and right in the second. Nevertheless, the skeptic argues that, as you have no way of separating the two scenarios, your belief in intersubjectivity could not possibly qualify as knowledge.

3    Applying Modal Logic to the Skeptical Scenario

In this section, I will give a brief introduction to modal logic and show how it applies to the skeptical scenario presented above. The idea of modal logic is to formalise a way of thinking that is very common among philosophers. It is a very useful tool for the philosopher to think about how the world could have been. In this way, the philosopher can reason about what is necessary and what is possible. Modal logic makes this reasoning formal by stipulating that when we reason about how the world could have been we are in fact thinking about other possible worlds. So, in the skeptical scenario, there are two possible worlds. There is the skeptical world where an evil scientist kidnaps you and your brain is hooked up to a supercomputer and there is the non-skeptical world where this does not happen and you live on as normal. The skeptic has argued that even if we live in the non-skeptical world, we cannot know this.

Let’s untangle this argument a bit. We will do so using epistemic logic, which is a branch of modal logic that reasons about knowledge. Before we can formalise the notion of knowledge we need the concept of epistemic accessibility. Imagine you are sitting in a lecture hall, and your mate turns to you and asks if you know whether it is raining outside or not. Not having looked at the weather forecast and sitting inside without any visual clues of the outside you admit that you do not know whether it is raining or not. Let’s also suppose that it is in fact raining. To formalise this, we say that there are two possible worlds that are completely identical bar the fact that in one of the worlds it is raining and in the other it is not raining. Your world happens to be the one where it is raining, but the world where it is not raining is still epistemically accessible from your world since there is nothing true in that world that contradicts what you know.

Now, your mate turns to you again and asks if you know whether Lucie will join you for lunch after the lecture. You, having just agreed to have lunch with Lucie, answer that yes you know that she will join you for lunch. We can now update our model by adding a third possible world where Lucie does not join you for lunch. However, this world is not epistemically accessible from your world as you know that she will join you for lunch, and so there is something that is true in that world that contradicts something that you know.

In general, we say that a world v is epistemically accessible from a world w for an agent just in case there is no statement X that the agent knows at w but is false at v. It is easy to see that any world must be epistemically accessible from itself as there is nothing you can know about a world that is false in that world. This is all we need to formally define knowledge. The formal definition of knowledge in epistemic logic is that an agent knows X at world w just in case X is true at all worlds that are epistemically accessible from w [1].

Returning to the skeptical claim, it can now be stated as the claim that the skeptical world is epistemically accessible from the non-skeptical world, and therefore that you cannot know the claim of intersubjectivity.

4    Refuting the Skeptical Claim using Modal Logic

In this section, we will refute the skeptic by using some modal logic or our own. Before we do this, I want to make a small observation. Notice that it is very plausible that the non-skeptical world is epistemically accessible from the skeptical world. In the skeptical world, we know very little. We don’t know that other people think like we do, since they are all simulated by the supercomputer. We don’t know that the hands we look down on are our own since again they are simulated by a supercomputer. In fact, one can argue that we have almost no knowledge of the external world in the skeptical world. We still believe all the same things that we believe in the non-skeptical world, but since all of those beliefs are false we cannot know then. Hence, since we know so little, the non-skeptical world must be epistemically accessible. This is because there is nothing in the non-skeptical world that refutes anything we know in the skeptical world, as we know so little.

This is not a very controversial observation, but it is very useful because now we can reformulate the skeptical claim. The skeptic claims that the epistemic accessibility is symmetric. A symmetric epistemic accessibility means that if v is epistemically accessible from w then w is epistemically accessible from v. Now the skeptic can argue that because the non-skeptical world is epistemically accessible from the skeptical world, and the epistemic accessibility is symmetrical, then the skeptical world has to be epistemically accessible from the non-skeptical world.

The rest of this section will be spent refuting the idea that epistemic assessability is symmetric. Now, in modal logic, accessibility has been studied extensively. There is a formal result from modal logic that we will use, but I will simplify it to stop this essay from being too technical. In our case, the result says that epistemic accessibility is symmetric just in case for every statement A, if A is true at a world w then we know that we cannot know that A is false [1]. Hence, the goal of this section is to argue that there can be a statement A such that it is true in the non-skeptical world, but we cannot know that we cannot know that A is false.

The first thing to establish is that there can be a sentence A which is true in the non-skeptical world but we believe it to be false. If this is not the case then we would know all and only those things that are true, which seems like too much to demand of humans. Further, when we believe something then we often believe that we know it. Hence, it is plausible to have a sentence A that is true but we believe that we know that it is false. We would like our beliefs to be consistent so that I cannot believe that it is raining and not raining at the same time. If this is the case then I cannot believe that I don’t know that A is false. The last thing to note is that if we know something then we believe it, so conversely if I don’t believe something then I cannot know it. Hence, since I don’t believe that I don’t know that A is false, then I don’t know that I don’t know that A is false. So, it is plausible that there is a sentence A that is true in the non-skeptical world but where I don’t know that I don’t know that A is false. This is precisely what we needed to show that epistemic accessibility is not symmetrical. This, in turn, makes the skeptical argument fall apart, as the skeptical world is not epistemically accessible from the non-skeptical world and hence we can have knowledge of other people’s subjectivity.

5    Conclusion

This essay aims to refute the skeptical scenario through the use of modal logic. This is done to give philosophical backing to an assumption that is widely accepted in the field of psychology. If the skeptics were right, and we could not know that other people think the same way we do, then several accepted psychological methods and practices would look dubious at best. Hence, the psychologist should feel some comfort that one worry about the legitimacy of psychology is put to rest.

References

[1] Wolfgang Schwarz. Logic 2: Modal logic, 2023.