Dreaming, Perception, and Knowledge in Plato’s Theaetetus and Vasubandhu’s Twenty Verses

In this chapter, I examine the relevance of the philosophical use of dreaming for the examination of the thesis that knowledge is perception. I begin by studying the position attributed to Protagoras in Plato’s Theaetetus, according to which the perceptual experiences we have when dreaming count as knowledge. I argue that this position requires two different subjects in the two different contexts of cognition (dreaming and waking). I suggest that Vasubandhu’s use of dreaming in the Twenty Verses — to show that perception without external objects is possible — can help make sense of Protagorean perception. I raise the problem that both positions struggle to align their metaphysics with the phenomenology of perception. With the help of dreaming, Vasubandhu can explain how transformation may yield perceptual knowledge (in the form of buddha-vision). No such transformation is possible for a Protagorean, because the different subjects inhabiting different cognitive contexts are not causally related.