1. Speech synthesis apparatus comprising: a dialog-style selection arrangement responsive to at least one factor affecting intelligibility of speech output as heard by a user, to select a dialog style intended to provide at least a minimum level of intelligibility; a speech-application text provider for providing text-form utterances for a current speech application in the dialog style selected by the selection arrangement; and a text-to-speech converter for converting text-form utterances received from the speech-application text provider into speech form.