forms from a proto-language was August Schleicher, in his Compendium der vergleichenden Grammatik der indogermanischen Sprachen, originally published in 1861. Proto-Indo-European Proto-Indo-European (PIE) is the linguistic reconstruction of the common ancestor of the Indo-European languages. August Schleicher's 1861 reconstruction of PIE was the first proposed proto-language to be accepted by modern linguists. More work has gone into reconstructing it than any other proto-language, and it is by far the best understood among all proto-languages of its age. During the 19th century, the vast majority of linguistic work was devoted to reconstruction of Proto-Indo-European or its daughter proto-languages such as Proto-Germanic, and most of the current techniques of linguistic reconstruction in historical linguistics (e.g., the comparative method and the method of internal reconstruction) were developed as a result. PIE must have been spoken as a single language or a group of related dialects (before divergence began), though estimates of when this was by different authorities can vary massively, from the 7th millennium BCE to the second. A number of hypotheses have been proposed for the origin and spread of the language, the most popular among linguists being the Kurgan hypothesis, which postulates an origin in the Pontic–Caspian steppe of Eastern Europe in the 5th or 4th millennia BCE. Features of the culture of the speakers of PIE, known as Proto-Indo-Europeans, have also been reconstructed based on the shared vocabulary of the early attested Indo-European languages. As mentioned above, the existence of PIE was first postulated in the 18th century by Sir William Jones, who observed the similarities between Sanskrit, Ancient Greek, and Latin. By the early 20th century, well-defined descriptions of PIE had been developed that are still accepted today (with some refinements). The largest developments of the 20th century were the discovery of the Anatolian and Tocharian languages and the acceptance of the laryngeal theory. The Anatolian languages have also spurred a major re-evaluation of theories concerning the development of various shared Indo-European language features and the extent to which these features were present in PIE itself. Relationships to other language families, including the Uralic languages, have been proposed but remain controversial. PIE is thought to have had a complex system of morphology that included inflectional suffixes as well as ablaut (vowel alterations, as preserved in English sing, sang, sung). Nouns and verbs had complex systems of declension and conjugation respectively. Arguments against an Indian origin of proto-Indo-European Diversity According