Editing Indo-European languages (section)

=== Satem and centum languages ===
{{Main|Centum and satem languages}}
[[File:Indo-European isoglosses.png|thumb|upright=1.6|Some significant isoglosses in Indo-European daughter languages at around 500&nbsp;BC.
{{Legend|#9fc7f3|Blue: centum languages}}
{{Legend|#ef7a6e|Red: satem languages}}
{{Legend|#f6a20f|Orange: languages with [[Augment (Indo-European)|augment]]}}
{{Legend|#a1f091|Green: languages with PIE *-tt- > -ss-}}
{{Legend|#f6d3ab|Tan: languages with PIE *-tt- > -st-}}
{{Legend|#fdd1d1|Pink: languages with instrumental, dative and ablative plural endings (and some others) in *-m- rather than *-bh-}}]]
The division of the Indo-European languages into satem and centum groups was put forward by Peter von Bradke in 1890, although [[Karl Brugmann]] did propose a similar type of division in 1886. In the satem languages, which include the Balto-Slavic and Indo-Iranian branches, as well as (in most respects) Albanian and Armenian, the reconstructed [[Proto-Indo-European phonology#Consonants|Proto-Indo-European palatovelars]] remained distinct and were fricativized, while the labiovelars merged with the 'plain velars'. In the centum languages, the palatovelars merged with the plain velars, while the labiovelars remained distinct. The results of these alternative developments are exemplified by the words for "hundred" in Avestan ({{lang|ae|satem}}) and Latin ({{lang|la|centum}})—the initial palatovelar developed into a fricative {{IPA|[s]}} in the former, but became an ordinary velar {{IPA|[k]}} in the latter.

Rather than being a genealogical separation, the centum–satem division is commonly seen as resulting from innovative changes that spread across PIE dialect-branches over a particular geographical area; the centum–satem [[isogloss]] intersects a number of other isoglosses that mark distinctions between features in the early IE branches. It may be that the centum branches in fact reflect the original state of affairs in PIE, and only the satem branches shared a set of innovations, which affected all but the peripheral areas of the PIE dialect continuum.{{sfn|Encyclopædia Britannica|1981|pp=588, 594}} Kortlandt proposes that the ancestors of Balts and Slavs took part in satemization before being drawn later into the western Indo-European sphere.{{sfn|Kortlandt|1990}}