The Centum-Satem division is an isogloss of the Indo-European language family, related to the evolution of the three dorsal consonant rows reconstructed for Proto-Indo-European, *kʷ (labiovelars), *k (velars), and *ḱ; (palatovelars). The terms come from the words for the number "one hundred" in representative languages of each group (Latin centum and Avestan satəm).
The Satem languages include Indo-Iranian, Armenian, Balto-Slavic, Albanian, and perhaps also a number of barely documented extinct languages, such as Thracian and Dacian. This group merged PIE-velars and PIE-labiovelars to develop into velars, and changed PIE-palatovelars into sibilants. Although Albanian is treated as a Satem language, there is some evidence that the plain velars and the labiovelars may not have been completely merged in Proto-Albanian.
The Centum group is often thought of as being identical to "non-Satem", i.e. as including all remaining dialects. However, this group features a merging of PIE-velars and PIE-palatovelars to velars in a separate Centum sound change, independent from and predating the Satem sound change. More specifically, in the sense of Brugmann's "languages with labialization", the Centum group includes Italic, Celtic, Germanic, Greek and possibly a number of minor and little known extinct groups (such as Ancient Macedonian, Venetic and probably the Illyrian languages). Tocharian combined all rows into a single velar row and although the relative chronology of the change is unknown, it lacks the assibilation typical of "Satem", thus is often considered "Centum".
The Proto-Anatolian language apparently did not undergo either the Satem or the Centum sound change. The velar rows remain separate in Luwian, while Hittite may secondarily have undergone a Centum change, but the exact phonology is unclear.
|Modern situation of the centum-satem isogloss (shown in red)|
August Schleicher in his 1871 Compendium assumes only a single velar row, k, g, gh. Karl Brugmann in his 1886 Grundriss accepts only two rows, denoting them q, g, gh "velar explosives" vs. k̑, g̑ and g̑h "palatal explosives". Brugmann terms the Centum languages "languages with labialization" or "u̯-languages" and the Satem languages "languages without labialization", and he opines that
The presence of three dorsal rows in the proto-language is not universally accepted. The reconstructed "middle" row may also be an artifact of loaning between early daughter languages during the process of Satemization. For instance, Oswald Szemerényi (e.g., in his 1995 Introduction), while recognizing the usefulness of the distinction *kʷ, *k, *ḱ as symbolizing sound-correspondences, argues that the support for three phonologically distinct rows in PIE is insufficient and prefers a twofold notation of *kʷ, *k. Other scholars who assume two dorsal rows in PIE include Kuryłowicz (1935), Meillet (1937), Lehmann (1952), and Woodhouse (1998).
The likelihood of three dorsal rows has also been disputed on typological grounds, but that argument has little merit, since there are, indeed, languages with such a three-row system, for example Northwest Caucasian languages such as Abkhaz, the Yazgulyam language (an Iranian language, but its system of dorsals is unrelated to PIE phonology), Hausa and Hopi.
The existence of this feature in Northwest Caucasian languages, added to the poor vowel system and glottalic consonants apparently shared between PIE and NW Caucasian, may hint at an early Sprachbund or substratum that reached geographically to the PIE homelands. This same type of languages, featuring complex verbs and of which the current Northwest Caucasian languages might have been the sole survivors, was cited by Peter Schrijver to indicate a local lexical and typological reminiscence in western Europe pointing to a possible Neolithic substratum.
The Satem shift is conveniently illustrated with the word for '100', Proto-Indo-European , which became e.g. Avestan satəm (hence the name of the group), Persian sad, Sanskrit śatam, Latvian simts, Lithuanian šimtas, Old Church Slavonic sъto etc., as contrasted with Latin centum (pron. [kentum]), English hund(red)- (with /h/ from earlier *k, see Grimm's law), Greek (he)katon, Welsh cant, Tocharian B kante, etc. Another example is the Latin prefix con- ("with"), which appears in Russian, a satem language, as so-; soyuz ("union") is in fact cognate with "conjoin".
The status of Armenian as a Satem language as opposed to a Centum language with secondary assibilation like e.g. French (i.e. the collapse of the velars with labiovelars rather than with the palatovelars) rests on the evidence of a very few words.
In the Centum languages, the palato-velar consonants merged with plain velars (*, *, *). Most of the Centum languages preserve Proto-Indo-European labio-velars (*, *, *) or their historical reflexes as distinct from plain velars; for example, PIE * : * > Latin c /k/ : qu /kʷ/, Greek κ /k/ : π /p/ (or τ /t/ before front vowels), Gothic /h/ : /hʷ/, etc.
Attestation of labiovelars as actual phonemes /kʷ/, as opposed to simple biphonematic /kW/ is attested in Greek (the Linear B q- series), Italic (Latin qu), Germanic (Gothic hwair ƕ and qairþra q) and Celtic (Ogham ceirt Q). Thus, while usually reconstructed for PIE, the labiovelar quality of this row may also be an innovation of the Centum group, causally related to the fronting of the palatovelars. The chief witness for this question is Anatolian, the phonology of which is for orthographical reasons not known in detail. Hittite (and Luwian) in any case chose not to use the existing cuneiform q- series (which stood for a voiceless uvular stop in Akkadian), but represents reflexes of PIE labiovelars as ku. Opinions on whether this represents an Anatolian single phoneme, or a group of /k+w/ are divided. There have been recent claims that the Bangani language of India contains traces of a Centum language, but they are widely considered spurious.
Incomplete Satemization in Baltic, and, to a lesser extent, Slavic, is taken as an indication of the diffusion of the satem sound change, or, alternatively, due to loans via early contact of Proto-Baltic and Proto-Germanic speakers. Examples of remnants of labial elements from labiovelars in Balto-Slavic include Lithuanian ungurys "eel" < *angʷi- , Lithuanian dygus "pointy" < *dʰeigʷ-, Fewer examples of incomplete Satemization are also known from Indo-Iranian, such as Sanskrit guru "heavy" < *gʷer-, kulam "herd" < *kʷel-; kuru "make" < *kʷer- may be compared, but they arise only post-Rigvedic in attested texts.
Whether areal or dialectal, the centum/satem distinction was long considered to represent a division of Proto-Indo-European into western and eastern zones. The example of Tocharian, though, has led to a competing view of the satem sound change as an innovation radiating outward from the central Indo-European language communities, but largely failing to reach the west-European or eastern (Tocharian) peripheries.