Historically, English syllabics have not evolved over time from native practice, but rather are the inventions of literate poets, primarily in the 20th century. Structurally, syllable counts are not bound by tradition, even very long lines are not divided into hemistichs, and the verse exhibits none of the markers usually found in other syllabic meters (with the occasional exception of end-rhyme), relying for their measure solely on total count of syllables in the line. Perceptually "it is very doubtful that verse lines regulated by nothing more than identity of numbers of syllables would be perceived by auditors as verse . . . Further, absent the whole notion of meter as "pattern", one may question whether syllabic verse is 'metrical' at all." In English, the difficulty of perceiving even brief isosyllabic lines as rhythmically equivalent is aggravated by the inordinate power of stressed syllables.