Abstract

The canonical version of external world scepticism has the following structure: Premise1: If P knows that she is not a brain in a vat, then P does not have knowledge of the external world. Premise2: P does not know that she is not a brain in a vat. Conclusion: Therefore, P does not have knowledge of the external world. Some philosophers attack premise1 by denying the underlying closure principle. I will investigate possible argumentations for and against premise2. I will show that premise2 is only true if additional internalistic conditions are fulfilled. I will conclude that the canonical version of the argument is inadequate and that premise1 must be replaced by a stronger internalistic premise. After presenting the adequate argument, I will argue that this internalistic premise contradicts the closure principle underlying premise1. I will conclude that external world scepticism can only hold if the closure principle is rejected.