Centum-Satem isogloss

Languages of the Indo-European family are classified as either centum languages or satem languages according to how the dorsal consonants (sounds of "K" and "G" type) of the reconstructed Proto-Indo-European language (PIE) developed. An example of the different developments is provided by the words for "hundred" found in the early attested Indo-European languages. In centum languages, they typically began with a /k/ sound (Latin centum was pronounced with initial /k/), but in satem languages, they often began with /s/ (the example satem comes from the Avestan language of Zoroastrian scripture).

The table below shows the traditional reconstruction of the PIE dorsal consonants, with three series, but according to some more recent theories there may actually have been only two series or three series with different pronunciations from those traditionally ascribed. In centum languages, the palatovelars, which included the initial consonant of the "hundred" root, merged with the plain velars. In satem languages, they remained distinct, and the labiovelars merged with the plain velars.

The centum–satem division forms an isogloss in synchronic descriptions of Indo-European languages. It is not thought that the Proto-Indo-European language split first into centum and satem branches from which all the centum and all the satem languages, respectively, would have derived. Such a division is made particularly unlikely by the discovery that while the satem group lies generally to the east and the centum group to the west, the most eastward of the known IE language branches, , is centum. Each of the ten branches of the Indo-European family independently developed its status as a centum or satem language.

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