 Perception Pn coheres with perceptions P1 through Pn−1 to the extent that the causal laws observed in P1 through Pn−1 are observed in Pn. This gives us reason to exclude hallucinatory perceptions from universal experience: hallucinatory perceptions involve apparent violations of the causal laws that are observed to hold in our “waking” perceptions, so they do not cohere with those other perceptions.