A theory of phonology that distinguishes between articulatory and perceptual representations and processes (Boersma 1998) accounts for the typological facts of nasal harmony more succinctly and with fewer assumptions for innate substantive devices, than theories that maintain a single kind of phonological features and a single phonological grammar, like the theories applied to nasal harmony by Piggott (1992), Piggott & Van der Hulst (1997), and Walker (1998). A functional account of multisegmental nasality leads us to identify two types: the articulatory spreading of velum lowering, which occurs in Piggott's type-A languages, and the perceptual harmony of nasality on the morpheme or word level, which occurs in Piggott's type-B languages. Generative accounts of nasal harmony have to take recourse to ad-hoc natural classes, exceptions to exceptions, grammaticization of constraints against unproducable perceptual output, functional exceptions to innate hierarchies, feature geometry, and multi-level OT. If all these things were really needed, UG would be full of substantive phonological detail. However, the functional approach to phonology can account for the facts of nasal harmony without assuming anything but general properties of human motor behaviour and perception. This is compatible with the view that the phonological part of the innate language device does not contain much more than: the cognitive abilities of categorization, abstraction, wild generalization, and extrapolation; the storage, retrieval, and access of arbitrary symbols; a stochastic constraint grammar; a gradual learning algorithm; laziness; the desire to understand others; and the desire to make oneself understood.