A well-known example is the similar tone systems in Sinitic languages (Sino-Tibetan), Hmong–Mien, Tai languages (Kadai) and Vietnamese (Mon–Khmer). Most of these languages passed through an earlier stage with three tones on most syllables (but no tonal distinctions on checked syllables ending in a stop consonant), which was followed by a tone split where the distinction between voiced and voiceless consonants disappeared but in compensation the number of tones doubled. These parallels led to confusion over the classification of these languages, until André-Georges Haudricourt showed in 1954 that tone was not an invariant feature, by demonstrating that Vietnamese tones corresponded to certain final consonants in other languages of the Mon–Khmer family, and proposed that tone in the other languages had a similar origin.