Proto-Indo-European language

Proto-Indo-European (PIE) is the reconstructed common ancestor of the Indo-European language family. Its proposed features have been derived by linguistic reconstruction from documented Indo-European languages. No direct record of Proto-Indo-European exists.

Far more work has gone into reconstructing PIE than any other proto-language, and it is the best understood of all proto-languages of its age. The majority of linguistic work during the 19th century was devoted to the reconstruction of PIE or its daughter languages, and many of the modern techniques of linguistic reconstruction (such as the comparative method) were developed as a result.

PIE is hypothesized to have been spoken as a single language from 4500 BC to 2500 BC during the Late Neolithic to Early Bronze Age, though estimates vary by more than a thousand years. According to the prevailing Kurgan hypothesis, the original homeland of the Proto-Indo-Europeans may have been in the Pontic–Caspian steppe of eastern Europe. The linguistic reconstruction of PIE has provided insight into the pastoral culture and patriarchal religion of its speakers.

As speakers of Proto-Indo-European became isolated from each other through the Indo-European migrations, the regional dialects of Proto-Indo-European spoken by the various groups diverged, as each dialect underwent shifts in pronunciation (the Indo-European sound laws), morphology, and vocabulary. Over many centuries, these dialects transformed into the known ancient Indo-European languages. From there, further linguistic divergence led to the evolution of their current descendants, the modern Indo-European languages. Today, the descendant languages of PIE with the most native speakers are Spanish, English, Portuguese, Hindustani ( Hindi and Urdu), Bengali, Russian, Punjabi, German, Persian, French, Marathi, Italian, and Gujarati.

PIE is believed to have had an elaborate system of morphology that included inflectional suffixes (analogous to English ''child, child's, children, children's'') as well as ablaut (vowel alterations, as preserved in English ''sing, sang, sung, song'') and accent. PIE nominals and pronouns had a complex system of declension, and verbs similarly had a complex system of conjugation. The PIE phonology, particles, numerals, and copula are also well-reconstructed.

Asterisks are used as a conventional mark of reconstructed words, such as *, *, or *; these forms are the reconstructed ancestors of the modern English words ''water'', '' hound'', and ''three'', respectively.

Development of the hypothesis

No direct evidence of PIE exists; scholars have reconstructed PIE from its present-day descendants using the comparative method. For example, compare the pairs of words in Italian and English: and ''foot'', and ''father'', and ''fish''. Since there is a consistent correspondence of the initial consonants that emerges far too frequently to be coincidental, one can infer that these languages stem from a common parent language. Detailed analysis suggests a system of sound laws to describe the phonetic and phonological changes from the hypothetical ancestral words to the modern ones. These laws have become so detailed and reliable as to support the Neogrammarian rule: the Indo-European sound laws apply without exception.

William Jones, an Anglo-Welsh philologist and puisne judge in Bengal, caused an academic sensation when he postulated the common ancestry of Sanskrit, Greek, and Latin in 1786, but he was not the first to state such a hypothesis. In the 16th century, European visitors to the Indian subcontinent became aware of similarities between Indo-Iranian languages and European languages, and as early as 1653, Marcus Zuerius van Boxhorn had published a proposal for a proto-language ("Scythian") for the following language families: Germanic, Romance, Greek, Baltic, Slavic, Celtic, and Iranian. In a memoir sent to the in 1767, , a French Jesuit who spent all his life in India, had specifically demonstrated the analogy between Sanskrit and European languages. According to current academic consensus, Jones's famous work of 1786 was less accurate than his predecessors', as he erroneously included Egyptian, Japanese and Chinese in the Indo-European languages, while omitting Hindi.

In 1818, Rasmus Christian Rask elaborated the set of correspondences in his prize essay ('Investigation of the Origin of the Old Norse or Icelandic Language'), where he argued that Old Norse was related to the Germanic languages, and had even suggested a relation to the Baltic, Slavic, Greek, Latin and Romance languages. In 1816, Franz Bopp published ''On the System of Conjugation in Sanskrit'', in which he investigated a common origin of Sanskrit, Persian, Greek, Latin, and German. In 1833, he began publishing the ''Comparative Grammar of Sanskrit, Zend, Greek, Latin, Lithuanian, Old Slavic, Gothic, and German''.

In 1822, Jacob Grimm formulated what became known as Grimm's law as a general rule in his . Grimm showed correlations between the Germanic and other Indo-European languages and demonstrated that sound change systematically transforms all words of a language. From the 1870s, the Neogrammarians proposed that sound laws have no exceptions, as illustrated by Verner's law, published in 1876, which resolved apparent exceptions to Grimm's law by exploring the role of accent (stress) in language change.

August Schleicher's ''A Compendium of the Comparative Grammar of the Indo-European, Sanskrit, Greek and Latin Languages'' (1874–77) represented an early attempt to reconstruct the proto-Indo-European language.

By the early 1900s, Ind