Centum and satem languages
An example of the different developments is provided by the words for "hundred" found in the early attested Indo-European languages (which is where the two branches get their names).
[1] The Anatolian branch probably falls outside the centum–satem division; for instance, the Luwian language indicates that all three dorsal consonant rows survived separately in Proto-Anatolian.
Historically, it was unclear whether the labiovelar row represented an innovation by a process of labialisation, or whether it was inherited from the parent language (but lost in the satem branches); current mainstream opinion favours the latter possibility.
Labiovelars as single phonemes (for example, /kʷ/) as opposed to biphonemes (for example, /kw/) are attested in Greek (the Linear B q- series), Italic (Latin ⟨qu⟩), Germanic (Gothic hwair ⟨ƕ⟩ and qairþra ⟨q⟩) and Celtic (Ogham ceirt ⟨Q⟩) (in the so-called P-Celtic languages /kʷ/ developed into /p/; a similar development took place in the Osco-Umbrian branch of Italic and sometimes in Greek and Germanic).
Linguist Wolfgang P. Schmid argued that some proto-languages like Proto-Baltic were initially centum, but gradually became satem due to their exposure to the latter.
It lost the labial element of PIE labiovelars and merged them with plain velars, but the palatovelars remained distinct and typically came to be realised as sibilants.
In the satem languages, the reflexes of the presumed PIE palatovelars are typically fricative or affricate consonants, articulated further forward in the mouth.
For example, the PIE root *ḱm̥tóm, "hundred", the initial palatovelar normally became a sibilant [s] or [ʃ], as in Avestan satem, Persian sad, Sanskrit śatam, sto in all modern Slavic languages, Old Church Slavonic sъto, Latvian simts, Lithuanian šimtas (Lithuanian is between Centum and Satem languages).
Another example is the Slavic prefix sъ(n)- ("with"), which appears in Latin, a centum language, as co(n)-; conjoin is cognate with Russian soyuz ("union")[citation needed].
"Incomplete satemisation" may also be evidenced by remnants of labial elements from labiovelars in Balto-Slavic, including Lithuanian ungurys "eel" < *angʷi- and dygus "pointy" < *dʰeigʷ-.
A few examples are also claimed in Indo-Iranian, such as Sanskrit guru "heavy" < *gʷer-, kulam "herd" < *kʷel-, but they may instead be secondary developments, as in the case of kuru "make" < *kʷer- in which it is clear that the ku- group arose in post-Rigvedic language.
[16] August Schleicher, an early Indo-Europeanist, in Part I, "Phonology", of his major work, the 1871 Compendium of Comparative Grammar of the Indogermanic Language, published a table of original momentane Laute, or "stops", which has only a single velar series (Reihe), *k, *g, *gʰ, under the name of Gutturalen.
[17][18] He identifies four palatals (*ḱ, *ǵ, *ḱʰ, *ǵʰ) but hypothesises that they came from the gutturals along with the nasal *ń and the spirant *ç.
[19] Karl Brugmann, in his 1886 work Outline of Comparative Grammar of the Indogermanic Language (abbreviated Grundriss), promotes the palatals to the original language, recognising two stores of Explosivae, or "stops", the palatal (*ḱ, *ǵ, *ḱʰ, *ǵʰ) and the velar (*k, *g, *kʰ, *gʰ),[20] each of which was simplified to three articulations even in the same work.
[21] In the same work, Brugmann notices among die velaren Verschlusslaute, "the velar stops", a major contrast between reflexes of the same words in different daughter languages.
In 1890, Peter von Bradke published Concerning Method and Conclusions of Aryan (Indogermanic) Studies, in which he identified the same division, as did Brugmann, but he defined it in a different way.
The latter distinction led him to divide the "palatal series" into a "group as fricative" (Spirant) and a "pure K-sound", typified by the words satem and centum respectively.
By the 1897 edition of Grundriss, Brugmann (and Delbrück) had adopted Von Bradke's view: "The Proto-Indo-European palatals ... appear in Greek, Italic, Celtic and Germanic as a rule as K-sounds, as opposed to in Aryan, Armenian, Albanian, Balto-Slavic, Phrygian and Thracian ... for the most part sibilants.
Both these theories have some support if PIE was spoken near the Caucasus, where both uvular and glottal consonants are common and many languages have a paucity of distinctive vowels.
There remain, however, several alternative proposals with just two rows in the parent language, which describe either "satemisation" or "centumisation", as the emergence of a new phonematic category rather than the disappearance of an inherited one.
