In this paper I offer an explanation of the ineffability (linguistic inexpressibility) of sensory experiences. My explanation is put in terms of computational functionalism and standard externalist theories of representational content. As I will argue, many or most sensory experiences are representational states without constituent structure. This property determines both the representational function these states can serve and the information that can be extracted from them when they are processed. Sensory experiences can indicate the presence of certain external states of (...) affairs but they cannot convey any more information about them than that. So, format- or code-conversion mechanisms that link different systems of representation (linguistic and perceptual) to each other will fail to extract any relevant information from sensory experiences that could be coded in language. They only way to establish specific roles for sensory experiences in communication and the organization of behavior is to attach to them, by associative links, words, or other behavioral responses. If a sensory experience has no linguistic label associated to it in a particular subject, then no linguistic description can token, or activate, that state in the subject. In other words, no linguistic description can cause a subject to undergo an unlabeled perceptual state. On the contrary, complex, or syntactically structured perceptual states can be built up, on the basis of descriptions, by mechanisms of constructive imagination (conceived here as one sort of format conversion). It is this difference between complex and unstructured representational states that gives us an understanding of the phenomenon we call the ineffability of qualia. (shrink)