Indo-European sound laws

As the Proto-Indo-European language (PIE) broke up, its sound system diverged as well, according to various sound laws in the daughter Indo-European languages.

Especially notable is the palatalization that produced the satem languages, along with the associated ruki sound law. Other notable changes are Grimm's law and Verner's law in Proto-Germanic; an independent change similar to Grimm's law in Armenian; loss of prevocalic *p- in Proto-Celtic; Brugmann's law in Proto-Indo-Iranian; Winter's law and Hirt's law in Balto-Slavic; and merging of voiced and breathy-voiced stops, and /a/ and /o/, in various "northern" languages. Bartholomae's law in Indo-Iranian, and Sievers' law in Proto-Germanic and (to some extent) various other branches, may or may not have been common Indo-European features. A number of innovations, both phonological and morphological, represent areal features common to the Italic and Celtic languages; among them are the development of labiovelars to labial consonants in some Italic and Celtic branches, producing "p-Celtic" and "q-Celtic" languages (likewise "p-Italic" and "q-Italic", although these terms are less used). Another grouping with many shared areal innovations is Greek, Indo-Iranian, and Armenian; among the common phonological innovations are Grassmann's law in Greek and Indo-Iranian, and weakening of pre-vocalic /s/ to /h/ in Greek, Iranian and Armenian.

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