Indo-European is a related group or family of languages spread over large parts of Asia and most of Europe. By modern colonization, it has also been carried over to the Americas, Australia and parts of Africa. It compromises a dozen major branches and several ill-defined minor groups. The term Indo-European or Proto-Indo-European also refers to the common ancestral language, spoken in later prehistory, from which the attested members of the family descend. This common language was necessarily the cultural property of a community, and information about the language can reveal a picture of that community. The principle of Proto-Indo-European and the Indo-European languages is essentially the same as that with Latin and the Romance languages of today (French, Italian, Spanish, and so on). In the case of Latin, we know that it was the language of ancient Rome, that it spread with military expansion of the Roman empire, and that it then broke up into local vernaculars in Europe after the Empire disintegrated. In the case of Indo-European, the common ancestor belonged to a much earlier horizon, before documentary records, and a process more or less analogous to that of the ebb and flow of Latin with the Roman Empire can only be inferred. Celtic is one of the branches of Indo-European, and all Celtic languages are also Indo-European languages. Using the model of a human family, we may think of the Celtic Languages as being more closely related to one another; for example, Irish and Welsh would be siblings. A Celtic language would be more distantly related to a non-Celtic Indo-European language; for example, Irish and Hindi would be cousins, but neither are related to Hungarian or Tamil. The existence of the Indo-European language family was already presumed by the first Europeans who learned Sanskrit, and anticipated by linguists of the 18th century. Sir William Jones (1746 - 94), a Judge in India during British rule and an expert on Indian languages. clearly articulated the theory of the common ancestry of Sanskrit, Greek and Latin. ( A non-Welsh-speaking Welshman, Cymro di-Gymraeg, Jones was introduced to the King of France by the British ambassador as 'a man who can speak all languages but his own'.) Since then further research has elucidated the principal details of the history of the whole group, and reconstructed the common ancestor, Proto-Indo-European. The workings of the Indo-European sound system are now understood in great detail. The morphology (i.e., such features as the personal and case forms of the verb and changes in the endings of the noun to express different grammatical functions) is known to a high degree, and much of the Proto-Indo-European vocabulary can be reconstructed with confidence. Basic patterns of Indo-European word order are implied by similarities in the early attested languages. Similarities in poetic formulae or stock phrases among such early texts as the Greek Iliad, the Vedic hymns, and Hittite religious formulae bring us to the threshold of recovering fragments of Proto-Indo-European traditional oral poetry. Indo-European is highly inflectional, and the grammatical elements (morphemes) usually express several functions at once. On the basis of the vocabulary of reconstructed Proto-Indo-European, we can gain an insight in to the culture of the people who spoke it. Some scholars favour a date for Proto-Indo-European in the 3rd millennium BC, while others believe that the branches must alrady have been seperated by 3000 BC. The speed of linguistic changes is unpredictable, and can vary tremendously between two neighbouring languages, or even within one single language. Social change often precipitates linguistic change; migration and substantial influence from other languages will also have effects. For example, English and Afrikaans have developed inflectional systems that are simpler than those of their relatives in the Germanic group. Fame, hospitality, and truth are pivotal for Indo-European ethics, as shown by the concord of early poetry in the early Indo-European branches. Celtic shares this heritage fully. Nevertheless, as we see from anthropology, comparative religion, and comparative literature, these values are not confined to people who speak Indo-European languages. Proto-Indo-European had three distinct sets of consonants similar in sound to the English k and (hard) g. In the 'palatal' set, the top of the tongue was placed farther forward to the top of the mouth, on the hard palate. In the 'velar' set, the tongue was farther back on the velum or soft palate. This difference can be felt by noting the different position of the tongue in the initial consonant of English palatal keel versus velar call, or palatal gill versus velar gull. A subgroup of Indo-European languages in the west, including Celtic, turned the IE palatals into velars. These are called centum languages, from the Latin word for 'hundred', pronounced /kentum/ in classical times, with an initial velar for an IE palatal; compare Welsh cant (also with k-) and Irish céad 'hundred'. In the satem group, the IE palatals have remained distinct from the velars. Proto-Indo-European also had a series of voiced aspirated consonants: bh, dh, g´h, gh, and gwh (similar to English 'subhuman', adhere, pig-headed, log-house, and egg white). According to the Kurgan hypothesis which is the one I personally subscribe to, this is the Indo-European Urheimat.