The voice user interface's (VUI) success hinges on its ability to elicit from the caller the specific responses that will enable the system to help solve a problem. While there's certainly consensus on such a fundamental principle, the conflict emerges at the skeletal level of VUI design, where three components should work in sync with one another. First are the grammars, which encompass all the possible things an end user might say. Second are the prompts, which the system says to provoke a caller response. Third is dialogue flow, which is the way the entire structure is organized. If a pattern of vocabulary-recognition errors emerges in which a segment of the population misinterprets a prompt and responds in an unrecognizable way, it's time to hone the system. Sometimes that means simply adding more grammars. Distinction needs to be drawn between providing instruction and building a feature that provides more detailed direction in navigating the system the moment the caller explicitly asks for it.