What kinds of mental states can be based on epistemic reasons? The standard answer is only beliefs. I argue that perceptual states can also be based on reasons, as the result of crossmodal interactions. A perceptual state from one modality can provide a reason on which an experience in another modality is based. My argument identifies key markers of the basing relation and locates them in the crossmodal Marimba Illusion (Schutz & Kubovy 2009). The subject’s auditory experience of musical tone (...) duration is based on the reason provided by her visual representation of the length of the musician’s gesture and other stored perceptual principles. (shrink)