Isochrony is a linguistic analysis or hypothesis assuming that any spoken language's utterances are divisible into equal rhythmic portions of some kind. Under this assumption, languages are proposed to broadly fall into one of two categories based on rhythm or timing: syllable-timed or stress-timed languages (or, in some analyses, a third category: mora-timed languages). However, empirical studies have been unable to directly or fully support the hypothesis, so the concept remains controversial in linguistics. While isochrony may be a useful theoretical framework in some contexts, studies suggest that, at best, syllable structure in natural speech only has a somewhat-regular rhythm.