
The Indo-European language family comprises a vast number of languages and dialects spoken throughout the world today. All of these languages are descended from a common ancestor known as Proto-Indo-European, which scholars estimate was spoken about six thousand years ago. This common ancestor has been reconstructed by historical linguists using the comparative method. Sound laws are regular instances of change to a language's phonological system, typically viewed as exceptionless under the Neogrammarian hypothesis. For example, the Romance languages, all descended from Latin, each have sound changes that affect the Latin c sound before a front vowel, leading to the pronunciation of [t͡ʃ] in Italian (cento, 'one hundred'; cielo, 'sky') but [s] in French (cent, ciel) and [θ] in European Spanish (cien, cielo). By tracking these kinds of changes, linguists can map out the relationships between languages with common origins.
This glossary provides a list of sound laws that have been formulated by linguists for the various Indo-European languages. It contains any named sound law which affects any of the major branches of the Indo-European family or more than one descendant language. Laws affecting one language may be included if a family has fewer than five well-attested members. While it is generally thought that the Anatolian languages broke off first, the internal relations of the other widely-accepted subfamilies – Albanian, Armenian, Balto-Slavic, Celtic, Germanic, Hellenic, Indo-Iranian, Italic, and Tocharian – are unclear and the subject of scholarly debate.







