Our beliefs about the external world seem vulnerable to sceptical worries provoked by standard sceptical scenarios in which we are dreaming, deceived by evil demons, or brains-in-vats. However, it is usually assumed that there is no equivalent problem of internal world scepticism. The standard sceptical scenarios don’t raise any worries about my beliefs about my experiences, or beliefs, for example. Indeed, it is often taken to be a constraint on an effective sceptical scenario that it preserves these aspects of my subjectivity.
My current research investigates the idea that, despite the prevailing assumption, there is a problem of internal world scepticism.
The first task of the project is to describe the problem of internal world scepticism. I start by considering Descartes’ famous claim that, notwithstanding sceptical worries, I can at least be certain that I am thinking, and therefore that I exist. There are two approaches to explaining the certainty of these beliefs. The first emphasises the special reflexive nature of the content of these beliefs. I argue that this explanation is unsatisfactory, because there are examples of beliefs with similarly reflexive content that are nevertheless subject to sceptical worries. The second emphasises the special phenomenal nature of the subject matter of these beliefs. Drawing on Lichtenberg and Hume, I argue that although this approach may be able to explain certainty that thinking is happening, it cannot explain certainty that there is an I who does that thinking. Insofar as beliefs about the internal world are committed to the existence of such an I, they are vulnerable to sceptical scenarios in which there is thinking, but no I. Thus we face the problem of internal world scepticism.
This does not yet show that the problem of internal world scepticism is on a par with the problem of external world scepticism. There may yet be an answer to the former that is not available to the latter, and this answer might preserve the idea that my beliefs about my internal world are immune to scepticism in a way that my beliefs about the external world are not. Where might this answer come from? One possibility is that it might be drawn from the distinctive nature of self-knowledge. However, I argue that no account of self-knowledge provides a distinctive answer to the problem of internal world scepticism. On the contrary, the only promising answers are given by externalist accounts of self-knowledge. This is a point in favour of externalist accounts of self-knowledge, but the answer to scepticism given by such accounts is analogous to popular responses to the problem of external world scepticism given by externalists about empirical knowledge.
Is there anything left of the idea that knowledge of the internal world is immune to scepticism? Not insofar as we consider beliefs about my internal world that imply the existence of an I, because it is this existential implication that is vulnerable to sceptical worries. But what about beliefs about my internal world that have no such existential implication? The final task of the project is to develop an understanding of such “impersonal” beliefs. While the phenomenological explanation fails to explain the certainty of beliefs that entail the existence of an I, it can explain the certainty of these impersonal beliefs. The resulting view has links with the Buddhist doctrine of anattā (the no self doctrine), and the philosophy of Lichtenberg.