Descartes states the relevant premise in terms of what we think of as dreams versus what we think of as waking: every sensory experience he thought he was having while awake he can also think of himself as sometimes having while asleep.

Much ado has been made about whether dreaming arguments are self-refuting. According to an influential objection, similarity theses presuppose that we can reliably distinguish dreams and waking – we need first to distinguish them, in order to compare them; yet the conclusion of dreaming arguments entails that we cannot reliably distinguish. Therefore, if the conclusion of such an argument is true, then the premise invoking the Similarity Thesis cannot be. Some formulations of dreaming arguments