The interval between two stressed syllables is equal (stress-timed).
The idea was first expressed thus by Kenneth L. Pike in 1945, though the concept of language naturally occurring in chronologically and rhythmically equal measures is found at least as early as 1775 (in Prosodia Rationalis). This has implications for linguistic typology: D. Abercrombie claimed "As far as is known, every language in the world is spoken with one kind of rhythm or with the other ... French, Telugu and Yoruba ... are syllable-timed languages, ... English, Russian and Arabic ... are stress-timed languages."
While many linguists find the idea of different rhythm types appealing, empirical studies have not been able to find acoustic correlates of the postulated types, calling into question the validity of these types. However, when viewed as a matter of degree, relative differences in the variability of syllable duration across languages have been found.
^Wells, John (2006). English Intonation: An Introduction. Cambridge University Press. p. 3. ISBN0-521-68380-7.
^Nespor, M., Shukla, M., & Mehler, J. (2011). Stress‐timed vs. syllable‐timed languages. In van Oostendorp et al. (Eds.), The Blackwell Companion to Phonology (pp. 1147-1159). Malden, MA: Blackwell.
^Pike, Kenneth L. (1945). The Intonation of American English, vol. 1. Ann Arbor: University of Michigan Press. pp. 34–35.
^Abercrombie, David (1967). Elements of General Phonetics. Edinburgh U.P. p. 97.